The description relates to controlling slagging and/or fouling in biomass burning furnaces. Combustion of such a biomass the fuel with air produces combustion gases containing sodium and/or potassium compositions, and the combustion gases are treated by contacting the combustion gases with kaolin and aluminum hydroxide. At least one of the kaolin and aluminum hydroxide can be introduced with the fuel, in a combustion chamber, with reburn fuel or with overfire air. For fuels also high in zinc and/or heavy metals, magnesium hydroxide is introduced into the combustion chamber or following heat exchangers.

The description relates to controlling slagging and/or fouling in biomass burning furnaces. Combustion of such a biomass the fuel with air produces combustion gases containing sodium and/or potassium compositions, and the combustion gases are treated by contacting the combustion gases with kaolin and aluminum hydroxide. At least one of the kaolin and aluminum hydroxide can be introduced with the fuel, in a combustion chamber, with reburn fuel or with overfire air. For fuels also high in zinc and/or heavy metals, magnesium hydroxide is introduced into the combustion chamber or following heat exchangers.

A method for controlling an NOx concentration in an exhaust gas in a combustion facility by: measuring a reaction velocity k.sub.i of each of a plurality of chars, each corresponding to a plurality of types of pulverized coals; determining a relationship between the NOx concentration in the exhaust gas and the reaction velocity k.sub.i for each of the chars; (iii) blending the plurality of the types of the pulverized coal, wherein a blending ratio of the plurality of the types of the pulverized coal is determined by using, as an index, a reaction velocity k.sub.blend of the char of the blended pulverized coal, which corresponds to a target NOx concentration or below, on the basis of the relationship; and supplying the blended pulverized coal to the combustion facility as the fuel of the combustion facility.

A method for controlling an NOx concentration in an exhaust gas in a combustion facility by: measuring a reaction velocity k.sub.i of each of a plurality of chars, each corresponding to a plurality of types of pulverized coals; determining a relationship between the NOx concentration in the exhaust gas and the reaction velocity k.sub.i for each of the chars; (iii) blending the plurality of the types of the pulverized coal, wherein a blending ratio of the plurality of the types of the pulverized coal is determined by using, as an index, a reaction velocity k.sub.blend of the char of the blended pulverized coal, which corresponds to a target NOx concentration or below, on the basis of the relationship; and supplying the blended pulverized coal to the combustion facility as the fuel of the combustion facility.

A method for controlling an NOx concentration in an exhaust gas in a combustion facility by: measuring a reaction velocity k.sub.i of each of a plurality of chars, each corresponding to a plurality of types of pulverized coals; determining a relationship between the NOx concentration in the exhaust gas and the reaction velocity k.sub.i for each of the chars; (iii) blending the plurality of the types of the pulverized coal, wherein a blending ratio of the plurality of the types of the pulverized coal is determined by using, as an index, a reaction velocity k.sub.blend of the char of the blended pulverized coal, which corresponds to a target NOx concentration or below, on the basis of the relationship; and supplying the blended pulverized coal to the combustion facility as the fuel of the combustion facility.

A combustion system including a fuel storage stores solid fuel, a supply device connected to the fuel storage, a combustion device combusts supplied solid fuel, and a prediction device for predicting a switching time for types of solid fuel supplied from the fuel storage to the combustion device via the supply device. The prediction device comprises at least one processor configured to acquire a level of solid fuel stored in the fuel storage, predict, as the switching time, a future time when a level obtained by extrapolating time-dependent change in decrease in the level of the solid fuel reaches a threshold value, and display the switching time on a display device.