(2) Turbine bearings and shaft: Horizontal split, ring oiled,
sleeve type, water cooled. Shaft shall be stainless steel or
chrome plated under the packing glands. Shaft seals shall be
segmented carbon rings with springs and stops.
(3) Speed governor: Variable speed oil relay, NEMA Class D,
governor for speed control and pneumatic operator to maintain an
adjustable, preset pump discharge header pressure by variation of
turbine speed. Input to the operator shall be a 20 to 103 kPa
(gage) 3 to 15 psig pneumatic signal.
Provide an
electro-pneumatic transducer to accept the 4 to 20 mA signal from
the control system controller specified in VAMS Section 15901N
CONTROLS AND INSTRUMENTATION BOILER PLANT.
(4) Emergency overspeed governor: Completely independent of the
speed governor and shall operate a separate trip valve.
(5) Insulation: Turbine shall be insulated and lagged by the
manufacturer as specified in Section 15080N MECHANICAL INSULATION.
2.14.3.3
Minimum Flow Protection for Boiler Feed Water Pumps
a.
Automatic flow control valve: Provide with each pump an automatic
bypass valve. Valve shall automatically program the recirculation
flow, the detection of low flow, the cycling of control valve and
pressure letdown for high pressure boiler feedwater return to the
feedwater heater. Bypass valve shall be cast steel with stainless
steel internals, and shall have a rating of not less than 2068 kpa
(gage) at 204 degrees C 300 psig at 400 degrees F. Valve shall
have a line size body with a one inch recirculation connection.
Provide pumps and turbine with all trimmings which the
manufacturer considers essential for proper operation of units.
b.
Boiler feedwater automatic recirculation system: (Option to
Automatic Valve). Provide a boiler feedwater automatic
recirculation system to protect the feedwater pumps at low flow
conditions. System shall be capable of recirculating the minimum
flow recommended by the pump manufacturer. System shall be an
engineered system consisting of the various functional components
specified or shall be a self-contained and self-powered mechanical
system. Components of the engineered system shall include a flow
transmitter with orifice in feedwater line, bypass flow controller
with bypass flow control valve, and a bypass pressure reducing
orifice.
(1) System bypass flow controller: Include detection of low flow
and modulation of a control valve in a bypass line returning to a
low pressure sink. Incorporate a pressure let-down feature or
device to reduce the pressure from the boiler feedwater pump
discharge pressure to that of the low pressure sink.
(2) System bypass control valve: Modulate to provide minimum
flow recommended by the pump manufacturer and to provide shutoff
or recirculation flow when feedwater flow to boilers exceeds the
minimum flow required for pump protection.
SECTION 15502N
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