OPERATION AND MAINTENANCE MANUAL
SECTION 3 OPERATION AND MAINTENANCE 3.1 GENERAL a. The operator
should be thoroughly familiar with the function and controls of the
steam generator components and auxiliary equipment before operating
the unit. The information given in this section is not intended to
be a detailed procedure for operation of the steam generator, but
is meant to serve as a guide together with the instructions of the
auxiliary equipment manufacturers and with knowledge derived from
initial unit operation. Circulating fluidized bed boilers are
chemical process reactors, without a defined fireball, which behave
differently than conventional boilers. They involve considerable
inertia of solids inventory and thermal energy. The operator should
be aware of the limitations imposed on the various parts of the
boiler and its auxiliaries and be alert to the actual operating
conditions during start-up and while operating per system demands.
Inert bed material such as sand can be used for initial start-up of
the unit. It is recommended to use saved, spent bed material for
subsequent start-ups. The startup bed material should be blown into
the lower furnace area with the PA, SA and ID fans running. Bed
material should be added until the static pressure of the bed is
4.5-5.5 KPa (18 22 w.g.) The saved bed material should be sampled
during any outage to check for any hardened material or for sticky
conditions due to absorbed moisture. Hydrated bed material can
break apart during start-up and increase fine bed material
carryover. The bed static pressure should be monitored during each
restart of the unit to see that the bed level is being maintained.
If bed static pressure decreases below the minimum value of 4.5 KPa
(18w.g.), additional start-up material should be added.
b.
c.
d.
e.
3-1(111455 Sec. 3)
OPERATION AND MAINTENANCE MANUALSECTION 3 3.2 PRECAUTIONS a.
Exposure to excessive negative or positive pressures can result in
serious damage to the unit and auxiliary equipment. Furnace draft
is monitored constantly and automatically controlled. Alarm and MFT
set points must be implemented. When a particular induced draft
(ID), primary air (PA) and/or secondary air (SA) fans(s) is to be
started, the corresponding inlet control vanes and outlet isolating
(shut-off) dampers (if supplied) should be closed. However, if
there are multiple fans, the dampers (and vanes) on the companion
idle fans should be open to assure a clear air flow path (between
ID, SA or PA fan inlet and stack) exists when starting the fans.
All safety valves are set by the manufacturer but should be
rechecked under actual operating conditions as the unit is being
brought up to pressure during initial operation. If a safety valve
does not lift at the pressure stamped on its nameplate or reseat
properly, the valve should be readjusted. In some localities, it is
required that only certain authorized personnel may change or
adjust safety valve settings or that changes in safety valve
settings be witnessed by authorized personnel. Consult governmental
and insurance requirements before changing the setting of any
safety valve. On installations where the safety valve relieving
pressure exceeds 8.274 MPa(g) (1200 psig), it is recommended that
checking and adjusting of safety valve settings prior to initial
operation be performed by the valve manufacturer service engineer.
A hydraulic or pneumatic device is recommended, if approved by the
inspecting authority, to assist in testing valves on 8.274 MPa(g)
(1200 psig) or higher installations. This device eliminates the
need for raising boiler pressure above normal and minimizes the
possibility of valve seat damage during testing.
b.
c.
Care should be exercised to insure that proper fuel-air ratio
for combustion is maintained. The Summary Performance Sheet in
Section 1 indicates the minimum excess air requirements. Operation
with less than the minimum expected excess air can be detrimental
from the standpoint of combustion, emission performance and safe
operation of the unit. For purposes of monitoring start-up
conditions during the life of the boiler, permanent thermocouples
are installed to measure metal temperature of various tubes. These
thermocouples are located in the unheated portion of the tubes
before they enter the outlet headers. The locations and quantities
are as follows: primary superheater (10), intermediate superheater
(16), finishing superheater (7), Reheater I (10) and Reheater II
(10). There are two (2) thermocouples on each cyclone outlet. There
are six (6) thermocouples on the steam drum. All these
thermocouples are to be used as aids in determining acceptable
firing rates during start-up. The unit can be operated up to the
temperature limits indicated in the table below. To protect the
equipment, the operator should correct any condition which has
caused an alarm to sound.
d.
e.
3-2(111455 Sec 3)
OPERATION AND MAINTENANCE MANUALSECTION 3 Location of Maximum
Maximum Temperatur Short Long Term e Term Temperature Measureme
Temperatu nt re* Primary Superheater Tubes to Outlet 487C (909F)
498C (928F) Header Intermediate Tubes to Outlet 596C (1105F) 604C
(1119F) Superheater Header Finishing Superheater Tubes to Outlet
600C (1112) 611C (1132F) Header Reheater I Tubes to Outlet 613C
(1135F) 627C (1161F) Header Reheater II Tubes to Outlet 610C
(1130F) 621C (1150F) Header * Short term means a period not
exceeding 4 hours per day. f. To prevent plugging, rusting,
oxidation and faulty operation of equipment, service air used on
the steam generator for operational purposes, whether for sealing,
aspirating, or atomizing, should be free of dirt, oil and water.
All high and low furnace pressure safety interlocks should be
checked for proper values and correct switching action and should
be in service before starting the induced draft fans. The automatic
furnace draft control equipment should be checked and ready for
service before starting the induced draft fans. Carbon monoxide
(CO) should be monitored continuously during operation of the steam
generator. Foster Wheeler recommends that CO monitoring equipment
be permanently installed for this purpose. It is strongly
recommended that the reliability of all drum level indicators be
checked at least once a shift. This would include all gage glasses
and remote level indicators. A water level indicator connection
that is being used to control water level should not be blown down
until the control is switched to another water level controller or
feedwater control is put on manual. On commonly operated valves,
such as superheater drains and vents, care should be taken maintain
the integrity of the root valves. These valves should never be in a
throttled position, and it may be beneficial to leave them open and
only close the end valves. The root valve would then only be closed
for end valve maintenance or downstream line maintenance. Both
valves on waterwall wall drains can be left closed. In all cases,
end valves should be closed before closing root valves and opened
only after opening the root valve in order to minimize potential
root valve seat damage. Section
g.
h.
i.
j.
3-3(111455 Sec 3)
OPERATION AND MAINTENANCE MANUALSECTION 3 k. Any of the
following operating conditions require mandatory MFT. The flow
rates and ratios are initial values and may be modified during
commissioning. Condition/Situation Drum Level Low-Low Drum Level
High-High Furnace Pressure High Furnace Pressure High-High Furnace
Pressure Low Furnace Pressure Low-Low Loop seal Header Pressure
LowLow Superheater/Waterwall Protection Cyclone Temperature >
Maximum Primary Air Flow < Minimum Instrument Air Pressure
Low-Low Total Air Flow < Minimum Air Fuel Ratio Low-Low No SA
Fan in Service No PA Fan in Service No ID Fan in Service Furnace
Bed Temperature HighHigh Furnace Bed Temperature Low Loss of all
Fuel BMS/DCS Communication Failure Emergency MFT Pushbuttons
Initiated Status -203 mm +203 mm +2.49 KPa +3.48 KPa -2.49 KPa
-3.48 KPa 25 KPa Cyclone Temp.>1000F and Steam Flow