Method for controlling the suspension in a suspension smelting furnace

A suspension smelting furnace for suspension smelting of pulverous solid matter, wherein the suspension smelting furnace comprises:

• a reaction shaft having an elongated vertical configuration and ending in a lower end,
• a lower furnace having an elongated horizontal configuration and that is in communication with and adjoins the lower end of the reaction shaft and
• a concentrate burner at the top of the reaction shaft,
• the concentrate burner comprises a pulverous solid matter supply device for feeding pulverous solid matter into the reaction shaft and comprises a gas supply device for feeding reaction gas into the reaction shaft,
• the concentrate burner being configured to feed pulverous solid matter and reaction gas into the reaction shaft to produce a suspension of pulverous solid matter and reaction gas in the reaction shaft,
• the lower furnace being configured to collect suspension on the surface of a melt in the lower furnace so that suspension that lands on the surface creates a collection zone at the surface of the melt in the lower furnace,
• the lower furnace further having a roof structure with a feed opening adjoining an open lower end of the reaction shaft,
• the suspension smelting furnace being configured to receive additionally to pulverous solid matter and additionally to reaction gas reducing agent from a reducing agent feeder,
• the reaction shaft being configured to receive fed pulverous solid matter and reaction gas into the reaction shaft by means of the concentrate burner so that suspension produced by pulverous solid matter and reaction gas forms a suspension jet in a suspension shaft, wherein the suspension jet widens in the reaction shaft in the direction of the lower furnace and wherein the suspension jet has an imaginary vertical central axis, and
• the suspension smelting furnace is capable of receiving the reducing agent in the form of a concentrated stream of reducing agent fed from the reducing agent feeder through the suspension in the suspension smelting furnace onto the surface of the melt to form a reducing zone containing the reducing agent within the collection zone of the melt, and wherein the reducing agent is fed at an initial velocity that is at least the feeding velocity of the reaction gas,
• the reducing agent feeder being configured so that a concentrated stream of reducing agent is directed from the reducing agent feeder essentially in the direction of an imaginary vertical central axis of the suspension jet and in the vicinity to the imaginary vertical central axis of the suspension jet to prevent reducing agent of the concentrated stream of reducing agent from reacting with reaction gas prior landing on the surface of the melt,
• wherein the reducing agent feeder is configured to feed the concentrated stream of reducing agent from the inside the lower furnace of the suspension smelting furnace.