Scale formation and growth when evaporating black liquor with high carbonate to sulphate ratio

• Scaling in black liquor evaporators has for longbeen recognised as a problem. Most problems are connected tothe precipitation of sodium salts. In the black liquor evaporation,as the black liquor gets concentrated, sodium carbonateand sodium sulphate will saturate and precipitate from the solution.When precipitation occurs the salts may crystallise on theheat transfer surface or adhere to the surface as well as they cancrystallise in the bulk. If crystals remain on the heat transfersurface an insulating layer of scales can quickly build up causingthe heat flux to drop and eventually forcing the evaporatorto be shut down for cleaning. The research in this paper focused primarily on scaling forblack liquors with high ratio of carbonate to sulphate, a conditionshown to be important in industrial black liquor evaporators(Frederick et al. 2004). The scaling behaviour was investigatedexperimentally in a falling film evaporator. The aim wasto find favourable operating conditions decreasing or eliminatingscaling. The examined parameters were different heat flux,circulation flow rate, internal residence time and black liquorfeed concentration. For the investigated operating conditions themain parameters affecting scaling were the circulation flow rateand heat flux whereas the scaling rate was seen independent ofthe internal residence time.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Pappers-, massa- och fiberteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Paper, Pulp and Fiber Technology (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Övrig annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Other Engineering and Technologies not elsewhere specified (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Kemiska processer (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Chemical Process Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

Fouling

Black liquor

Dicarbonate

Scaling

Evaporation

Falling film

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