Power Plant Fire Protection System (Part-II of III)
This section covers the water-based fire protection system
known as the hydrant system, used in thermal power plants.
Flow Scheme for a Typical 660 MW Unit
Hydrant System
Hydrant system shall consist of a fire water ring main network of
piping along with:
Isolation gate valves installed above ground on RCC pedestals
around areas to be protected.
Hydrant valves (external/internal)
Hose cabinets
Couplings
Branch pipe
Nozzles and water monitors along with all accessories.
Other accessories like MS painted hose box shall be provided
as per TAC.
External hydrants, hose houses, or hose boxes should be
located around the building perimeters, while internal hydrant
hose boxes should be placed at each staircase landing.
Fixed Water Monitors (outdoor type) shall be provided for:
ESP areas,
Boiler house
Tall building
Coal stock pile area
Bunker building
Junction tower/transfer towers and
Other areas in the coal conveyor at locations where water
can’t reach from hydrant system.
Hydrant System Requirements
Hydrant system requirements shall be designed keeping the
following aspects of design in mind in line with the TAC
requirements:
The hydrant network shall be sized to ensure that about 3.5
Kg/cm2 pressures are available at the hydraulically remotest
point (as per TAC) in the system with the hydrant pump
discharging the flow at rated pump capacity and head.
The velocity in the hydrant main shall not exceed 5.0 m/s.
At least two hydrants shall be provided with separate ring
main for the main plants.
Spacing of each outdoor hydrant shall be provided 45 meters
distance. The internal hydrant/landing valves shall be
provided 45 meters distance in case of TG halls, Mill
bay, Boiler and other area 30 Meters distance at each floor
space.
Building shall be deemed to be protected by a hydrant if the
hydrant is within 15 meters of the building.
Each of the landing valves and external hydrant valves
associated with the main plant like transformer yard, TG
building and Boiler area to be provided with a hose box.
Each ring mains to be terminated with an isolation valve and a
blind flange at all the corners to enable future
expansion/modification.
Fire water booster system pump head shall be designed for
farthest top most point of the boiler and pressure will be
tested at that elevation.
All the landings of boiler staircase, turbine buildings and other
multi-storied structures, coal handling plant transfer
points/junction towers, crusher house, bunker floors and other
auxiliary buildings/non-plant buildings shall be provided with
landing valves with hose box including the hose reels.
Spray System
The spray system operates automatically. Deluge valves are
controlled by fire detection devices, like quartzite bulb detectors,
and the system can be pressurized up to the deluge valves.
It covers all transformers located area, turbine and its auxiliaries,
all oil storage tanks, cooling units and purifiers units. The
equipment used in the whole system is spray pumps, the pressure
controlling unit, variety of valves and strainers. There are two
methods of spray system:
1. High Velocity Water spray system (HVWS system)
2. Medium Velocity Water spray system (MVWS system)
High Velocity Water Spray System (HVWS)
HVWS shall be designed as per TAC regulations. HVWS shall
consists of above group piping, along with relevant fittings, deluge
valves, isolation gate valves, spray nozzles, Quartzite bulb detector
and pressure switches. HVWS system shall be equipped with the
provision of automatically detect, control & extinguish any outburst
of fire. The system shall allow hydraulically open the deluge valve
thus allowing water to be sprayed on the equipment/area through
projector nozzles in the form of a solid conical emulsifying spray.
Isolation gate valve and y-type strainer shall be provided on
upstream and downstream side of the deluge valve. Fast acting
butterfly valve shall be provided as a by-pass to deluge valve, so
that this valve can be kept closed and can be operated manually in
case of malfunction of deluge valve.
The pressure at the hydraulically most remote point in the network
shall not be less than 3.5 bars for outdoor transformers as per TAC.
Placing of spray nozzles shall be such that their spray nozzles
should cones overlap each other.
