Automatic Fire Extinguishing System for Diesel Generator Room Part 2

In the previous article, we introduced the comparison and selection of automatic fire extinguishing systems and the design parameters in the design of the automatic fire extinguishing system for diesel generator rooms. In this article, Dingbo Power will continue to introduce the selection and relevant calculations of water mist nozzles, the layout of water mist nozzles, and other related matters for the automatic fire extinguishing system of the generator room.

1. Selection and Related Calculations of Water Mist Nozzles

Select the ZSTWB33.7/90 centrifugal atomizing open-type water mist nozzle (with a filter, made of brass). The rated working pressure is 0.35 MPa, the flow rate is 63 L/min, the atomization angle is 90°, the flow coefficient is 33.7, the connection thread is Rp3/4, the effective range is 2.5 m, the maximum horizontal spraying height is 1.9 m, and the water droplets are relatively fine. It is suitable for extinguishing liquid and electrical fires.

(1) The number of nozzles N=(S×W)/q=29.8≈30N = (S×W)/q = 29.8 \approx 30N=(S×W)/q=29.8≈30

SSS -- Protection area (m2m^2m2)

WWW -- Design spray intensity (L/(min×m2)L/(min×m^2)L/(min×m2))

qqq -- Flow rate of the water mist nozzle

(2) Consider that the minimum safety distance between the nozzle and the exposed part of high-voltage electrical equipment is 0.3 m, and enough space for personnel operation should be reserved. Each protected surface is treated as a plane. The water mist nozzles are arranged in a rectangular pattern. The installation angle of the side-spray nozzles is 30° (with respect to the horizontal direction), and the nozzle spacing should not be greater than 1.4 times the radius of the bottom circle of the water mist cone.

The radius of the bottom circle of the water mist cone R=B×tan⁡(Q/2)R = B×\tan(Q/2)R=B×tan(Q/2)

BBB -- Distance from the water mist nozzle to the protected object

QQQ -- Atomization angle of the water mist nozzle

2. Layout of Water Mist Nozzles and Others

(1) According to the layout of the diesel power station, 30 water mist nozzles are arranged. In addition, 3 nozzles are installed in the fuel tank room for protection. There are a total of 33 nozzles. The calculated second flow rate is 34.65 L/s, the designed second flow rate is 38.1 L/s, the diameter of the fire water inlet pipe is DN150, and the designed flow velocity is 1.98 m/s < 5 m/s. For the layout of water mist nozzles, see Figure 1.

(2) In this design, the ZSFY/SL-S360 (DN150) deluge valve set is selected, which includes a hydraulic alarm bell, pressure switch, deluge alarm valve, inlet signal valve, pressure gauge, test valve, and test signal valve, etc. A maintenance valve and a filter are installed in front of the valve. The pore size of the filter screen is 4.0 - 4.7 meshes per square centimeter. The pipeline after the filter is an internal and external hot-dip galvanized steel pipe, connected by threaded joints.

(3) The deluge valve has three starting methods: solenoid valve start, on-site manual start, and non-electric remote manual device start. In this design, a heat detector is used. After detecting and confirming the fire, the fire control linkage controller starts the solenoid valve. The control equipment is installed in the fire control room.

(4) If the sprayed water cannot be drained in time after the automatic fire extinguishing system is activated, it may cause the fire to spread and increase the difficulty of fire fighting. Therefore, a cast iron drain floor drain is installed in this design, and a fire-blocking water seal is also set up to prevent the fire from spreading along with the water flow.

(1) Since the shape of the diesel generator is irregular, calculations should be carried out according to the actual shape of the generator set. The water mist nozzles should be arranged in a three-dimensional layout method to ensure that each protected surface has sufficient water spray protection intensity.

(2) The main water supply pipe of the water spray system should preferably be arranged in a ring-shaped pipe network at the top, which can reduce the pressure difference between nozzles and make the sprayed water mist more uniform and effective.

(3) The water spray fire extinguishing system features fast startup, environmental friendliness, and low water consumption. It can meet the fire extinguishing requirements of diesel generator rooms. Moreover, its installation, operation, and pipeline layout are simple, and the cost is relatively low. Multiple control methods can effectively ensure the safety of fire protection.

Dingbo Power was founded in 1974 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to [email protected] we will pay highly attention on your question.