Reference Manual

18−4
are used for furnace walls and have a very short
lance with a nozzle at the tip. The lance rotates as
it moves into the furnace and cleans the deposits
from the wall in a circular pattern. Retractable
sootblowers are used in high flue gas temperature
zones. These operate the same as the wall
blower, but the lance is inserted into the boiler to
clean the internal tubes and can be partially or
fully retractable. Partially retractable sootblowers
are used where sootblower materials can
withstand the flue gas temperature.
Design Considerations:
D Noise and vibration
D Tight shutoff (Class V)
D High cycling operation
D Typical service conditions are 800-1200 psig
at 300-500 °F
Typical Specifications:
D easy-e, HP, or EH
D Whisper Trim
D FIELDVUE digital valve controller with low
travel cutoff
Optional:
D Oversized stem/VSC and/or welded stem
connection
Steam Turbine Generators
The majority of steam from the high pressure
header is used by large power generating steam
turbines. Most mills use a backpressure turbine(s)
(discharges to a lower pressure process header)
and at least one condensing turbine (discharges to
a condenser). Extraction steam from the turbines
is used to supply the medium and low pressure
process headers. These headers typically operate
at 400-600 psig and 60-150 psig respectively.
Pressure reducing valves are also used between
headers to balance demand vs. extraction or to
provide process steam during a turbine outage. If
desuperheating is required, a steam conditioning
valve is recommended for this service.
While electrical power produced by the turbines
(typically 30-70 MW) is important to mill
operations, supplying the process with steam is of
primary concern. Most mills are connected to a
local utility and purchase the balance of electrical
power required. By nature, the back pressure
turbine provides more than double the utilization of
available fuel energy as the condensing turbine.
The majority of steam discharged from the back
pressure turbine is utilized by process, while the
latent heat in the steam of the condensing turbine
exhaust is wasted in the condenser.
Main Steam PRV and Turbine
Bypass
Control of steam pressures and temperatures are
likely the most critical applications in a pulp and
paper mill. Steam is used for wood chip
preparation, process heating, pulp and paper
drying, boiler cleaning, energy production, and in
many other applications. Without steam, a pulp
and paper mill cannot operate. To accommodate a
variety of steam pressure requirements most sites
utilize three headers; high (1000-2000 psig),
medium (500 psig), and low (100 psig) pressure.
The power and recovery boilers supply high
pressure, high temperature steam to the high
pressure header. Much of the high pressure steam
undergoes a pressure reduction and is directed to
the medium and low pressure headers. When
demand for low pressure steam is high, the
medium pressure header also supplies steam to
the low pressure header.
Main Steam PRV
Pressure reduction between headers can be
achieved through the use of a pressure reducing
valve (PRV) or a steam turbine (also called turbo
generator). Main steam PRVs are often used to
bridge the high (1000-2000 psig), medium (500
psig), and low (100 psig) pressure headers. Each
PRV can perform only a single pressure reduction,
so multiple PRVs are required.
Design Considerations:
D High pressure and temperature
D Noise and vibration
D Tight shutoff (Class V)