Method of producing pulp and burning waste liquor obtained thereby

Claim 2

In a process for producing pulp, in which a cellulose feed stock is cooked in an aqueous liquor containing sulphur, and the resulting waste liquor is burnt in a furnace in order to recover chemicals which are used for preparing cooking liquor to be recycled in the process, the steps of: a. introducing an iron compound into the furnace, together with, or in parallel to the waste liquor; b. reacting said iron compound within the furnace with the sulphur constituent in the burning waste liquor to form a smelt containing an insoluble iron sulphide; c. removing said smelt from the furnace and dissolving said smelt in an aqueous solution to form a weak liquor for recycling in the process; d. separating said insoluble sulphide from said solution; e. reacting said separated iron sulfide with sulphuric acid to produce FeSO 4 and H 2 S, and separating said FeSO 4 and H 2 S; and reacting the FeSO 4 with NH 4 OH to obtain ammonium sulfate, (NH 4 ) 2 SO 4 , and iron hydroxide, Fe(OH) 2 , and recycling the latter as the iron compound to be introduced into the furnace.

Claim 3

The process according to claim 1, including the further step of reacting the ammonium sulfate in a distillation column under elevated pressure and temperature to cause a decomposition thereof into ammonia and sulphuric acid, and using this acid for reacting with the iron sulfide separated from the recycling process.

Claim 4

In a process for producing pulp, in which a cellulose feed stock is cooked in an aqueous liquor containing chlorine, and the resulting waste liquor is burnt in a furnace in order to recover chemicals which are used for preparing cooking liquor to be recycled in the process, the steps of: a. introducing an aluminum compound into the furnace together with, or in parallel to the waste liquor; b. reacting said aluminum compound within the furnace with the chlorine constituent of the burning waste liquor to form combustion gases carrying returnable process chemicals and aluminum chloride, said aluminum chloride being volatile at the elevated temperature prevailing in the furnace; c. removing said combustion gases from the furnace and separating off said returnable process chemicals from the combustion gases while the same still are at an elevated temperature; and thereafter d. removing said aluminum chloride from the combustion gases at a lower temperature.

Claim 5

In a process for producing pulp, in which a cellulose feed stock is cooked in an aqueous liquor containing chlorine, and the resulting waste liquor is burnt in a furnace in order to recover chemicals which are used for preparing cooking liquor to be recycled in the process, the steps of: a. introducing an aluminum compound into the furnace together with, or in parallel to the waste liquor; b. reacting said aluminum compound within the furnace with the chlorine constituent of the burning waste liquor to form combustion gases carrying returnable process chemicals and aluminum chloride, said aluminum chloride being volatile at the elevated temperature prevailing in the furnace; c. removing said combustion gases from the furnace and separating off said returnable process chemicals from the combustion gases while the same still are at an elevated temperature; and thereafter d. removing said aluminum chloride from the combustion gases at a lower temperature.

Claim 6

The process according to claim 3, including removing the aluminum chloride from the combustion gases by scrubbing with water, reacting the resulting aqueous solution with slaked lime to obtain calcium chloride and aluminum hydroxide separating said calcium chloride and recycling the aluminum hydroxide as the aluminum constituent for introduction into the furnace.

Claim 7

In a process for producing pulp in which a cellulose feed stock is cooked in an aqueous liquor containing sulphur and chlorine, and the resulting waste liquor is burnt in a furnace in order to recover chemicals which are used for preparing cooking liquor to be recycled in the process, the steps of: a. introducing an iron compound and an aluminum compound into the furnace together with, or in parallel to the waste liquor; b. reacting said iron compound with the sulphur constituent in the burning waste liquor, and said aluminum compound with the chlorine constituent of the burning waste liquor, within the furnace to form a smelt containing an insoluble iron sulphide and combustion gases carrying returnable process chemicals and aluminum chloride, respectively, said aluminum chloride being volatile at the elevated temperature prevailing in the furnace; c. removing said smelt from the furnace and dissolving said smelt in an aqueous solution to form a weak liquor for recycling in the process; d. separating said insoluble sulphide from said solution; e. removing said combustion gases from the furnace and separating off said returnable process chemicals from the combustion gases while the same still are at an elevated temperature; and thereafter f. removing said aluminum chloride from the combustion gases at a lower temperature.

Claim 8

In a process for producing pulp in which a cellulose feed stock is cooked in an aqueous liquor containing sulphur and chlorine, and the resulting waste liquor is burnt in a furnace in order to recover chemicals which are used for preparing cooking liquor to be recycled in the process, the steps of: a. introducing an iron compound and an aluminum compound into the furnace together with, or in parallel to the waste liquor; b. reacting said iron compound with the sulphur constituent in the burning waste liquor, and said aluminum compound with the chlorine constituent of the burning waste liquor, within the furnace to form a smelt containing an insoluble iron sulphide and combustion gases carrying returnable process chemicals and aluminum chloride, respectively, said aluminum chloride being volatile at the elevated temperature prevailing in the furnace; c. removing said smelt from the furnace and dissolving said smelt in an aqueous solution to form a weak liquor for recycling in the process; d. separating said insoluble sulphide from said solution; e. removing said combustion gases from the furnace and separating off said returnable process chemicals from the combustion gases while the same still are at an elevated temperature; and thereafter f. removing said aluminum chloride from the combustion gases at a lower temperature.

Claim 9

The process according to claim 5, wherein said iron compound is Fe(OH) 2 , said aluminum compound is AlO(OH), and said iron and aluminum compounds are mixed with said waste liquor prior to introduction into said furnace.