Reference Manual

10B −18
pulp. The pressure drop is from digester pressure
to atmospheric in the blow tank.
As in the top circulation line, there are two
isolation valves against digester pressure. There is
a large isolation valve between the digester
pressure and the blow unit. If the blow unit is
empty and the valve is opened under full digester
pressure, the sudden surge severely damages the
blow unit and valves. The blow unit must,
therefore, be filled with liquor and pressurized
before the large valve can be opened in a similar
manner to the top circulation lines. A pressure
switch prevents the valve from opening until the
blow unit pressure is increased to at least 175
psig.
The pulp flows to the blow tank, which is simply a
storage tank with a predetermined retention time,
before it goes to the next stage in the pulping
group, pulp washing and high density storage.
Valve: HV-87 Blow line pressurization
This valve provides dilution and pressurization in
the blow line prior to the opening of the blow valve.
D Typical process conditions:
— Fluid: Washer filtrate
— T = 170_F
— P = 225 – 350 psig
— dP = 10 – 50 psid
— Q = 165 gpm
D Typical valve selection:
— It is typically a NPS 2 valve. Kamyr has
specified a V300 valve with stainless steel
body and ball. The valve should be offered
with a Nitronic 50 shaft, PEEK bearings, and
an HD metal seal. A piston actuator is
normally specified.
Valve: FV-12A Blow line flow control
D Typical process conditions:
— Fluid: High consistency pulp (10%)
— T = 180_F
— P = 170 psig
— dP = 80 psi
D Typical valve selection:
— The requirement for full bore is based on
the potential for plugging as large deposits
come out of the digester. This is a very
demanding and critical loop. The shape of
opening and flow area of the V300, by
design, has a lower potential for plugging
than a full bore valve. Recommended valve
construction includes: SST body with alloy 6
insert, alloy 6 V-notch, alloy 6 taper key,
alloy 6 silver plated bearings, alloy 6 HD
seal, and PTFE ENVIRO-SEAL packing. An
oversized, piston actuator is also suggested.
In addition, the valve should be sized to
operate at >60% opening.
Valve: FV-12B Blow line flow control
D Typical process conditions:
— Fluid: High consistency pulp (10%)
— T = 180_F
— P = 170 psig
— dP = 80 psi
D Typical valve selection:
— The requirement for full bore is based on
the potential for plugging as large deposits
come out of the digester. This is a very
demanding and critical loop. The shape of
opening and flow area of the V300 valve, by
design, has a lower potential for plugging
than a full bore valve. Recommended valve
construction includes: SST body with alloy 6
insert, alloy 6 V-notch, alloy 6 taper key,
alloy 6 silver plated bearings, alloy 6 HD
seal, and PTFE ENVIRO-SEAL packing. An
oversized piston actuator is also suggested.
In addition, the valve should be sized to
operate at >60% opening.
Valve: HV-81B Blow line isolation valve
This valve is an on/off valve that serves to isolate
the digester blow line.
D Typical valve selection:
— It is specified by Kamyr as a full bore ball
valve.
Valve: HV-90A and B Blow line
isolation valves
D Typical process conditions:
— Fluid: High consistency pulp (10%)
— T = 180_F
— P = 70 psig
— dP = 4 psi
D Typical valve selection:
— These valves are generally the same
valves as the flow control valves with the
exception that they are often one line size
larger and used for isolation only. These