Medium as it rotates submerged in slurry, is then washed and continuously

scraped from the surface of the disc at 60–70% dry solids. The lime mud is then

Discharged through a number of chutes into the mud mix tank. The washing step

Leads to a minor dilution of the white liquor, but reduces the requirements of

Downstream lime mud washing.

Fig. 9.14 A pressure disk filter [18].

The examples of equipment solutions described above are what will most likely be

Found in a new mill. Existing causticizing plants are likely to appear quite different, as

They may have seen certain pieces of equipment taken into different service over time

As causticizing capacity increased. Equipment with potential application in changed

Positions includes rotary drum filter for the washing of dregs or lime mud; candle

Filters for white liquor filtration or lime mud washing; and sedimentation clarifiers

For clarification of green liquor or white liquor, or for lime mud washing.

Lime Cycle Processes and Equipment

Lime mud from the white liquor filter is pumped to storage and then washed on a

Rotary drum filter for the removal of soluble liquor constituents. The wash filtrate

resulting fromlimemud washing, termed “weakwash”, is used for smelt dissolving.

The lime mud coming from the lime mud washer contains 75–85% dry solids.

It is either dried with flue gas in a separate, pneumatic lime mud dryer or is fed

Directly to the rotary kiln for drying and subsequent calcination. The diagram in

Fig. 9.15 shows how solids and gas flow countercurrently through a lime kiln

With a drying zone. Lime mud enters the refractory lined kiln at the cold end. The

Kiln slopes towards the firing end, and the solids move downwards as the kiln

Recovery

Slowly rotates. At first, water is evaporated from the lime mud in the drying section,

And then the carbonate is brought to calcination temperature in the heating

Zone; finally, the calcination reaction takes place in the calcination zone. The high

Lime temperature at the firing end causes agglomeration and slight sintering. The

overall retention time in the lime kiln is typically 2–4 h. Before leaving the kiln,

The lime is cooled in tubular satellite coolers and in turn heats up fresh combustion

Air. After that, the larger lime particles are crushed and the lime is stored in a

Silo for re-use in slaking.

The quality of the burned lime is characterized mainly by the amount of residual

calcium carbonate, typically 2–4%, and by the lime availability – that is, the

percentage of lime which reacts with acid, typically 85–95%. Lime make-up

requirements are usually in the range of 3–5%.

1.000

1.500

2.000

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