METHOD AND APPARATUS FOR PROCESSING BLACK LIQUOR OF PULP MILL Russian patent published in 2015 - IPC D21C11/12 D21C11/00 

FIELD: chemistry.

SUBSTANCE: invention relates to a method and an apparatus for processing black liquor of a pulp mill for recovering energy and chemicals therefrom. A method of processing black liquor of a pulp mill for recovering chemicals and energy contained therein includes steps of feeding black liquor into a pyrolysis reactor having a substantially oxygen-free chamber, wherein temperature in the pyrolysis reactor is maintained in the range of 400 to 600°C, feeding into the pyrolysis reactor causticising material which consists of sodium oxide (Na₂O) and a metal oxide (M_xO_y) comprising at least one of the following metal oxides: titanium oxide (TiO₂), iron oxide (Fe₂O₃) and manganese oxide (Mn₂O₃),where said causticising material is heated in a furnace unit where temperature is maintained in the range of 600 to 1000°C, leading to gasification of black liquor and formation of gaseous components and a residual solid substance, feeding the gaseous components formed in the pyrolysis reactor for further recycling, transporting the solid substance formed in the pyrolysis reactor into the furnace unit, where fuel contained therein is burnt using oxygen contained in air fed into the furnace unit, leading causticising material consisting of sodium oxide (Na₂O) and a metal oxide (M_xO_y), returning part of the causticising material formed in the furnace unit into the pyrolysis reactor and transporting part of it into a dissolving tank, where water is added, to form sodium hydroxide (NaOH) and a metal oxide (M_xO_y), returning the formed sodium hydroxide (NaOH) into the pulping process and at least the main part of the remaining metal oxide (M_xO_y) into the furnace where it forms causticising material with sodium oxide (Na₂O). The apparatus for processing black liquor of a pulp mill for recovering chemicals and energy contained therein includes a furnace unit, a pyrolysis reactor into which black liquor is fed and where the black liquor undergoes pyrolysis in a chamber which is substantially oxygen-free, and forms gaseous components and a solid substance, wherein temperature in the pyrolysis reactor ranges from 400 to 600°C, an apparatus for feeding gaseous components formed in the pyrolysis reactor for recycling, an apparatus for transporting solid substances formed in the pyrolysis reactor into the furnace unit, wherein temperature in the furnace unit ranges from 600 to 1000°C, where combustible material burns to form furnace gas, and caustic material forms, which consists of sodium oxide (Na₂O) and a metal oxide (M_xO_y), an apparatus for feeding part of the causticising material heated in the furnace unit into the pyrolysis reactor and feeding part into the dissolving tank to form sodium hydroxide (NaOH) and a metal oxide (M_xO_y) comprising at least one of the following metal oxide: titanium oxide (TiO₂), iron oxide (Fe₂O₃) and manganese oxide (Mn₂O₃), and an apparatus for transporting sodium hydroxide (NaOH) back into the pulping process and at least one main part of the remaining metal oxide (M_xO_y) into the furnace unit, where it forms causticising material with sodium oxide (Na₂O).

EFFECT: use of the method and apparatus can avoid the use of an exhaust-heat boiler in the whole process.

18 cl, 2 dwg