operation shall be from the local control panels as specified herein. Main
FGD system control panelboard shall interface with local controls as
specified paragraph entitled "Instrumentation and Controls." Once a
feeder/slaker has been selected for operation from the local control panel,
the lime slurry preparation equipment shall function automatically. A low
level signal from the slurry tank level switch shall start water feed, lime
feed, bin vibrator and other equipment as required including slaker
agitator and grit removal equipment. A high-level signal from the slurry
tank shall stop line feed and bin vibrator immediately and provide
continued operation of water feed, slaker agitator and grit removal
equipment for adjustable time periods. Provide control panels at the time
slurry preparation area enclosure preparation area enclosure and shall
include complete controls for equipment in the slurry preparation system.
In addition to selector switches or push buttons for all equipment, the
local controls shall provide full instrumentation to annunciate any
component failures and automatically trip equipment. Local annunciator
shall be provided for component faults including high slaker temperature,
slaker overflow, slaker fail-to-start grit remover zero speed, slurry
agitator zero speed, and low-low slurry tank level. Any local alarm shall
register at the main FGD system panelboard in steam plant. Flushing of the
slurry pumps and piping systems shall be controlled from a panel at the
slurry tank level in the lime system enclosure.
2.12.1.2
Spray Dryer Absorbers
The following paragraphs provide a typical functional description of the
control of sulfur dioxide concentration and flue gas temperature leaving
the spray dryer absorbers. It is recognized that individual differences
between control schemes may exist to the extent that not all of the control
details specified are applicable to a given system. The [proposal] [bid]
shall clearly indicate such differences and shall include a detailed
description of the control system features provided to attain the control
objectives specified in these paragraphs. The degree of sulfur dioxide
control achieved in the spray dryer absorber and fabric filter baghouse is
directly related to the rate of lime feed to the atomizer. The lime slurry
feed rate to the atomizer shall be regulated by a control valve which is
modulated by a signal from the analog control system utilizing an input
from an sulfur dioxide analyzer located at the fabric filter baghouse
outlet. The control valve shall fail closed on loss of air, power, or
control signal and the control system shall be provided with sufficient
interlocks so that FGD system upsets cannot result in excessive liquid feed
and subsequent moisture carryover to the fabric filter baghouse. The
control system shall be designed to automatically control the sulfur
dioxide concentration leaving the fabric filter baghouse at a level set by
the operator from an operating station in the control room. Provide
continuous indication of the inlet and outlet sulfur dioxide concentration,
control valve status and slurry feed rate on the main control panelboard.
The temperature of the flue gas leaving the absorber shall be controlled to
an operator-adjustable setpoint by automatic regulation of water feed to
the atomizer. The water feed rate to the atomizer shall be regulated by a
control valve which is modulated by a signal from the analog control system
utilizing an input from a temperature transmitter located at the spray
dryer outlet. The control system shall provide a means of assuring that
the outlet temperature remains above the moisture dewpoint with an adequate
margin of safety as required to prevent condensation at any point
downstream in the FGD system. A control signal will be available to
indicate the initiation and termination of the steam sootblowing cycle. The
temperature control system shall make use of this signal to automatically
compensate for the additional moisture input with the flue gas. The water
SECTION 15864N
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