Power Plant Fire Protection System (Part-III of III)
This section comprises of water based fire protection system which comprises of Medium velocity water spray (MVWS) system in thermal power plants.
Representation of MVWS Protection System
MVWS System Applications
Medium velocity water spray system shall be designed to protect the following:
- Cable gallery and cable spreader room in the main plant area
- ESP control room
- Switch yard room
- Ash handling plant area
- Coal handling plant area
- Water treatment plant area
- Circulating water pump area
- Sea water intake area
- Fuel oil pump house
- Switch yard and control room building
- All coal conveyor gallery in tunnels/underground and above ground
- Coal transfer points and junction towers
- Crusher house
- Emergency DG Building
- Fuel oil pump house (loading and unloading areas)
- Fuel oil storage tanks
MVWS System Design Requirements
Medium velocity water spray system design requirements MVWS system shall be designed as per TAC regulations. The medium velocity spray system shall consists of a network of open spray nozzles fitted with a special deflector to give required angle of discharge for the water around the area mentioned above.
The sprayers shall discharge a cone of water spray consisting of medium size droplets of water. The water supply to the MVWS system shall consists of a network of open spray nozzles fitted with a special deflector to give required angle of discharge for the water around the area to be protected. The water supply to the MVWS system shall be controlled by a deluge valve which shall operate electrically actuated solenoid valve on release of water pressure.
In order to avoid total flooding of the entire area of cable gallery/ coal conveyor system, the area to be protected by shall be divided into number of zones. Each zone shall have separate water supply network controlled by a deluge valve. A fire detection system provided for the MVWS protected area shall sense fire and shall actuate the deluge valve. In the event of fire in one zone, the deluge valve of the corresponding zone and those of adjacent zones on either side shall be opened.
MVWS System for Cable Galleries
The cable galleries shall have number of rows of cable trays and each row will have number of tiers of cable trays. Each of the cable rows shall be provided with a network of water distribution piping and nozzles. The distribution network shall consist of distribution header for each row of cable tray and on these headers drop pipes shall be provided so as to cover all the tires. In case of fire in the cable gallery, addressable multi-sensor detector supplemented with linear heat sensing cable of digital type shall be used for detection of fire. Upon detection of fire MVW spray system shall be brought into operation by automatically opening of deluge valve, which shall allow the projectors located in that area to direct water in the form of spray, which which will cut of oxygen supply and extinguish the fire. As per TAC regulations the density of spray water system in cable galleries shall be 12.2 lpm/m2 of the surface area for spray system. The pressure at the hydraulically most remote projector in the network shall not be less than 2.8 bar.
MVWS System for coal conveyors
MVWS for coal conveyors shall be provided for both top and return conveyors. Junction tower/Transfer tower, crusher house and all other areas shall also be covered.
Fire in the caol conveyor will be detected by the linear heat sensing cables and infrared ember detectors which shall provide signal for electrical actuation for deluge valve.
MVWS system spray nozzles shall be provided in row centre of the conveyor belt for top conveyor and on either side of the conveyor at 4 meters intervals. Staggering of sprayers are recommended for bottom conveyors. Conveyor walk way shall not be affected by MVWS system pipe routing.
As per TAC regulations the density of spray water system in coal conveyors shall be 10.2 lpm/m2 of the surface area for spray system. Hydraulically remotest sprayer shall have the minimum-pressure 1.4 bars, however the pressure at the hydraulically favorable sprayer shall not exceed 3.5 bars.
MVWS System for fuel oil pump house and EDG building
MVWS system for fuel oil pump house and Emergency DG (EDG) building shall be designed considering the pump house as a single zone. A network of pipes with spray nozzles shall be located near the roof of the pump house which shall be connected to a deluge valve.
The fire in fuel oil pump house and Emergency DG (EDG) building shall be detected by a detection-system comprising of quartzoid bulb detector which shall actuate the delude valve. Probe type heat detector shall be used for detection of fire on the fuel oil storage tanks.
As per TAC regulations the density of spray water system in Fuel oil pump house and Emergency DG set building shall be 10.2 lpm/m2 of the surface area for spray system. The pressure at the hydraulically most remote projector in the network shall not be less than 1.4 bar and 2.8 bar.
As per TAC the density of spray water for fuel oil storage tank shall be 3 lpm/m2 of surface area.