Reference Manual

13−4
fresh water spray may also be used for further
washing of cooking chemicals from the lime mud.
The dewatered lime mud is removed with a
scraper blade and the filtrate sent to a mix tank
feeding the lime mud washer (or pressure filter).
The operation is very similar to the dregs precoat
filter.
Valve: FV-10 Dilution water for lime
mud transfer
D Typical Process Conditions:
— Fluid: Clean condensate
— T = 176°F
— P = 30 - 40 psig
— ΔP = 5 - 10 psig
D Typical valve selection:
— NPS 2 carbon steel valves with 316
CRPL ball and TCM plus seat to achieve
class VI shutoff. Depending upon process
conditions, the Control-Disk could serve
as a great alternative.
Valve: FV-11 Lime Mud to Filter
D Typical process conditions:
— Fluid: Clean condensate
— T = 176°F
— P = 50 - 60 psig
— ΔP = 5 - 10 psig
D Typical valve selection:
— These valves can range from NPS 4 to
NPS 10. A SST body with 316 CRPL ball,
alloy 6 hard faced seat and alloy 6
bearings should be used in this
application.
Lime Recovery
Lime recovery, lime reburning, or calcining are
terms commonly used to describe this portion of
the chemical recovery cycle. As mentioned earlier,
the lime recovery area accepts the lime mud
(CaCO
3
) from the lime mud filter and converts it to
lime (CaO) for use in the slaker. This solves any
problems associated with lime mud disposal and
also has a significant economic impact by
reducing the need to purchase lime. With lime
recovery, purchased lime is only required to make
up system losses.
The conversion of the lime mud to lime is usually
accomplished in a rotary lime kiln. A rotary kiln is a
large steel tube lined with refractory bricks. The
cylinder is mounted on an incline, supported on
rollers, and rotated at a slow speed with an
electric motor/gear reducer set.
The lime kiln accepts the lime mud from the lime
mud filter at 60-70% solids. It is conveyed from
the upper to lower end by the rotation of the kiln. A
burner, utilizing oil or gas, is installed at the lower
end. The heat of the flame evaporates the
remaining moisture and yields lime and carbon
dioxide from the lime mud. This process also
causes the lime mud powder to agglomerate into
pellets which can be handled.
The lime product is conveyed to a storage silo for
use in the slaker. A scrubber is also used to
alleviate the dusting and pollution problem
associated with the exiting flue gas.
Valve: FV-12 Natural gas to lime kiln
burner
D Typical process conditions:
— Fluid: Fuel gas
— T = 86°F
— P = 50 - 60 psig
— ΔP = 1 - 3 psig
D Typical valve selection:
— NPS 4 carbon steel valves with 316
CRPL ball and TCM plus seat to achieve
class VI shutoff. Depending upon process
conditions, the Control-Disk could serve
as a great alternative.
Valve: FV-13 Fuel Oil to lime kiln
burner
D Typical process conditions:
— Fluid: Fuel Oil
— T = 260°F
— P = 210 - 220 psig
— ΔP = 20 - 25 psig
D Typical valve selection:
— These valves are usually NPS 2 carbon
steel valves with SST internals.