US 5,716,496 A · Method and apparatus for treatment of black liquor

Abstract

A method and an apparatus are provided for controlling crystallization (and thus preventing harmful fouling of heat transfer surfaces) during the treatment of black liquor. The black liquor is concentrated to a high dry solids content (at least about 70%, e.g. about 75-90%) in a falling film crystallizing apparatus (e.g. falling film evaporator). A part of the liquor flowing from the heat transfer surfaces and collected in a retention vessel (e.g. an interior volume of the evaporator) is recirculated to the heat exchange surfaces and a part of the liquor is discharged for further treatment (e.g. combustion in a recovery boiler). A part of the black liquor in the recirculation system is returned directly to the retention vessel in order to facilitate mixing and thus to bring about, in the retention vessel, crystallization of inorganic salts of the black liquor that is as complete as possible. Some of the discharged black liquor also may be returned, and a mixer and/or baffles disposed in the retention tank, to further enhance mixing.

Claims20

Dependent claims

A method of treating black liquor to produce black liquor having a dry solids concentration of at least about 70% utilizing a falling film concentrator including heat transfer surfaces, a retention tank, and a re-circulating system for returning black liquor from the retention tank to a top portion of the filling film concentrator, comprising the steps of:

(a) introducing black liquor having inorganic salts into the top portion of the falling film concentrator to fall in a film down the heat transfer surfaces, and pass to the retention tank;
(b) recirculating a first portion of the black liquor from the retention tank to the top portion of the falling film concentrator through the re-circulating system;
(c) withdrawing a second portion of the black liquor from the retention tank to effect further treatment thereof;
and
(d) returning a part of the first portion of black liquor in the recirculation system directly to the retention tank so as to enhance mixing within the retention tank so as to substantially complete crystallization of the inorganic salts of the black liquor in the retention tank so that fouling crystallization of salts on the heat transfer surfaces is minimized.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for treatment of black liquor

Life of this patent

Method and apparatus for treatment of black liquor

Life of this patent

Abstract

Claims20