Discussion on fire control and automatic control d

2022-09-22
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Discussion on fire control and automatic control design of large oil tank farm Abstract This paper analyzes and discusses the specific problems existing in the fire control system of large oil tank farm, and explains the necessity of reforming the fire control system of large oil tank farm and setting up the automatic fire control system. At the same time, a reasonable and reliable design scheme is put forward, and the design process and problems needing attention are introduced in detail. With the development of China's petroleum industry and the increase of crude oil and refined oil reserves, there are more and more large oil depots and oil tank farms in China. Most of such tank farms are reconstructed and expanded, and the fire control means still remain in the original manual operation. Due to the large number of oil tanks, the number of equipment and valves to be controlled is large, the operation time is long, and the process is complex, which is very prone to misoperation, and the safety of the oil tank farm is difficult to ensure

1 project overview

an oil tank farm in China was built in the 1970s and expanded into the existing scale in three phases. At present, there are five 20000 m3 steel floating roof tanks and four 50000 m3 steel floating roof tanks in the tank farm, with a storage capacity of 300000 m3. The reservoir area covers an area of 148000 m2. The original fire-fighting system is fixed cooling water and fixed foam fire-fighting system, including a fire pump room, two 1000 m3 fire-fighting water pools, tank farm fire pipes, tank fire-fighting system, etc. The fire pump room is equipped with three fire pumps, one 14sh - 6 pump is a foam mixture pump, one 12sh - 6 pump is a cooling water pump, and another 14sh - 6B pump is a public standby pump. The motors of the above pumps are 6000 V high-voltage motors. All equipment, valves, tank area partition valves and upper tank control valves in the pump room are manually controlled. See Figure 1 for the layout of the existing tank area and pump room

2 original operation mode and existing problems

original operation mode of fire protection system: when a fire occurs in the tank farm, the fire watch personnel immediately notify the substation watch personnel to switch on the power supply after receiving the fire alarm (it is stipulated that the high-voltage equipment cannot be normally closed); Notify the fire watch personnel after the substation watch personnel switch on; The fire watch personnel shall conduct the test jump and turning, and then notify the substation when everything is ready; Under the supervision of the personnel on duty of the substation, start the pump and outlet valve one by one, and the whole process takes 5 minutes. At the same time of the above operations, a fire watchman who is particularly familiar with the fire control process (to ensure no misoperation) must quickly run to the tank farm, close the corresponding foam mixture and cooling water partition block valve according to the different fire tanks, and then open the foam upper tank control valve and cooling water upper tank control valve. The 9# tank farthest from the fire pump room is the most unfavorable point for fire protection, and the above operation process takes 12 minutes after actual measurement. In addition, whether the third tank can work normally, the time for foam and cooling water to be put on the tank is about 1 min. it takes a total of 13 min to put foam mixture and cooling water on the tank to extinguish and cool the tank. There are the following problems:

(1) the tank farm is too large, and the fire cannot be found in time by manual fixed-point patrol inspection

(2) there is no guarantee that the fire extinguishing system will be started immediately after the fire is found, which will delay the fire fighter. Fire fighting depends on speed, and the fire-fighting system built in the early stage of the station is not suitable for the fire-fighting requirements of larger and larger tank farms. According to the information, once the oil tank fires, the temperature of the tank wall rises rapidly, and the strength of the oil tank steel plate decreases rapidly. If the temperature of the tank wall rises to 700 ℃, the strength of the oil tank steel plate will be reduced by more than 90%. At this time, the oil tank will be deformed and cracked. Once the high-temperature crude oil spills, the consequences are unimaginable. The fire is easy to extinguish in the initial stage, and the longer the time is, the harder it is to control the fire

(3) in case of fire, more than one person is required to participate in the operation. In the fire pump room, there must be at least two people on duty in each shift to ensure emergency treatment in case of fire, and they have nothing to do at ordinary times, which is a very contradictory problem in management

(4) if a fire occurs in an oil tank, the fire cannot be controlled in time, and then affect other oil tanks. If a fire event similar to Huangdao Oil Depot occurs, the loss is quite huge, so we cannot ignore it

3 transformation design

in view of the above reasons, in order to ensure safe production, the fire protection system transformation design was carried out for the tank farm

in the code for fire protection design of crude oil and natural gas engineering and the code for design of oil depots, there are no clear provisions on the fire control mode of the oil tank farm with a single tank capacity of less than 100000 m3, but a large number of oil tanks and a large total storage capacity. In view of the fact that the reservoir area has a large capacity and a large number of oil tanks, an automatic fire control system has been added to the design after communicating with Party A

key points of the fire protection system design:

(1) selection of the location of the fire pump room: according to the current situation of the oil tank layout in the oil tank area, the location of the fire pump room is comprehensively determined by considering the layout of the fire pipeline, the fire partition of the oil tank, the general layout and other factors

(2) calculate the design consumption of foam mixture and cooling water required for a fire in the storage tank according to the largest storage tank, and select the equipment according to the comprehensive consideration of meeting the fire extinguishing foam mixture and cooling water at the most unfavorable point for 5 minutes

(3) recheck the capacity of the fire pool according to the actual design cooling water spray volume of the largest tank

(4) the pump outlet valve, the control valve of the foam mixture and cooling water upper tank, and the control valve of the main partition are electric valves that can be remotely controlled to realize centralized control in the fire control room

(5) install combustible gas alarms in the tank farm, and set temperature sensing cables on each tank. When the temperature reaches the alarm set value, the alarm signal is transmitted to the fire control room through cable. When the operators in the fire control room receive the alarm signal, they use the television monitoring system to manually confirm the fire, so as to put out the fire in time

(6) the fire control room is equipped with an automatic fire control system to realize the automatic detection and control functions of fire operation procedures

(7) the tank farm is equipped with an industrial television monitoring system, a camera is set in the tank farm, and a monitor is set in the fire duty room. The personnel on duty monitor the tank farm all day long, so as to detect and alarm the fire in time

the above key points are described in detail below

3.1 determination of the location of the new fire pump room

we can see from Figure 1 that the location of the original fire pump room is inappropriate. According to the layout of tank farm and general layout, it is determined to build a new fire pump room and fire pool at the northeast corner of 2 # tank and 6 # tank

3.2 fire fighting zones

combined with the current layout of the tank farm and the location of the new fire pump room, on the premise of minimizing the full length of the pipeline, the oil tanks in the tank farm are divided into two independent fire fighting zones, with 1 # ~ 5 # tank (20000 m3 tank farm) as a zone; 6 # ~ 9 # tanks (50000 m3 tank farm) are a partition. The specific zoning method is shown in Figure 1. In this way, when the 50000 m3 tank farm is on fire, only the first partition can be filled, and when the 20000 m3 tank farm is on fire, only the second partition can be filled, and the two partitions do not affect each other. The full capacity is reduced, which is conducive to pump selection

3.3 determination of fire pipe diameter in tank farm

the pipe diameter of each partition can be determined according to the cooling water volume and foam mixture volume required for fire fighting of the largest tank in each partition, and when one pipeline is damaged, the other pipeline can meet the requirements of all fire water volume

as there are two independent zones, the first zone determines the pipe diameter according to the cooling water volume and foam mixture volume required by 50000 m3 tank fire fighting. In the second division, the pipe diameter is determined according to the cooling water volume and foam mixture volume required by 20000 m3 tank fire fighting

3.4 pump selection

the maximum volume tank in the tank farm is 50000 m3, the demand for foam mixture is 320m3/h, and the demand for cooling water is 490m3/h. According to article 7.4.6 of the code for fire protection design of crude oil and natural gas engineering, double pipes at the outlet of the fire pump are required to be connected with the ring to ensure that when one pipe is damaged, the other pipe can pass through all the fire water. After calculation, the full volume of foam mixture in the first zone is 90 m3, that is, within the first 5 minutes after starting the pump, the flow of foam mixture pump should reach 1080 m3/h to meet the requirements. By analyzing these data, one 300s90 (q = 790 m3/h, H = 90 m, P = 320 kW) pump and one dk400-11 (q = 368 m3/h, H = 103 m, P = 190 kW) pump can be selected as the foam mixture pump. In this way, when any oil tank is on fire, start two pumps to fill at the same time, stop 300s90 pump after 5 minutes, and run dk400 - 11 to meet the fire extinguishing requirements

50000 m3 tank fire fighting, the cooling water demand is 490 m3/h, and the cooling water filling capacity of the first zone is 130 m3, that is, in the first five minutes after starting the pump, the cooling water pump flow should reach 1560 m3/h. select one 300s90 pump (q = 790 m3/h, H = 90 m, P = 320 kW) and one 300s90b pump (q = 720 m3/h, H = 67 m, P =220 kW) respectively. In this way, when any tank is on fire, start two pumps at the same time to fill the cooling water pipe, and stop the 300s90 pump five minutes later, Running 300s90b pump can meet the cooling requirements. Then select one 300s90 pump as the public standby pump. The above pumps are equipped with 380 V low-voltage motor, which is convenient for operation and management

3.5 selection of foam proportioning device

due to the large range between the pipeline filling volume and the normal fire flow, the flow adjustable range of the selected proportioner should be able to adapt to this change, and at the same time, the equipment suitable for automatic control should be selected. In the actual design, two 10 t tank pressure proportioning devices are selected, and the flow of a single proportioner is 20 ~ 160 L/s

3.6 valve selection

main control valves such as pump outlet valve, main pipe control valve, partition control valve and upper tank control valve are all electric butterfly valves, which can be remotely controlled in the fire duty room

3.7 determination of the volume of the fire pool

the cooling water mode of the oil tank is the fixed water curtain sprinkler cooling system. The cooling water demand of the 50000 m3 tank during fire fighting is 136 l/s, and the cooling water demand of 4 hours is 1960 m3. When 50000 m3 tanks are used for fire fighting, the water demand for preparing foam mixture is 200 m3, and the water filling volume in the pipe is 220 m3. Therefore, the minimum water demand for one-time fire fighting is 2340 m3, and one 1000 m3 and one 2000 m3 fire water pool need to be built respectively

3.8 main process of the new fire protection system (see Figure 2)

process description of the new fire protection system: ① pump 1 and pump 2 are foam mixture pumps, pump 4 and pump 5 are cooling pumps, and pump 3 is a public standby pump. ② The pump inlet valve is normally open. ③ The pump outlet valve, main pipe control valve, tank farm partition valve and upper tank control valve are normally closed. ④ When the oil tank in the first zone (50000 m3 tank farm) is on fire, start the cooling water pump and foam mixture pump respectively, open the outlet valve of the corresponding pump and the partition valve of the first zone, and then open the control valve of the corresponding foam mixture and cooling water tank on the fire tank, which starts to extinguish and cool the oil tank. ⑤ When the oil tank in the second partition (20000 m3 tank farm) is on fire, start the cooling water pump and foam mixture pump respectively, open the outlet valve of the corresponding pump and the partition valve of the second partition, and then open the control valve of the corresponding foam mixture and cooling water tank on the fire tank, which starts to extinguish and cool the oil tank

3.9 monitoring system

three groups of cameras are set in the tank farm, and the control room is equipped with a monitoring screen. In the duty room, the personnel on duty can control the camera 360 to rotate and monitor the target. In this way, the situation of the whole tank farm can be seen at a glance on the monitoring screen

3.10 automatic fire detection system

set a circle of temperature sensing cable along the tank wall on the floating plate of each tank. In case of fire, due to the temperature rise, the resistance of the temperature sensing cable at the fire point becomes smaller, and quickly send a fire alarm signal to the duty room; Combustible gas alarm shall be set in the tank farm. After the personnel on duty confirm the fire through the monitoring system, the fire fighting system shall be started to extinguish the fire

3.11 automatic fire control program

PLC is used to collect and program all combustible gas signals, temperature sensing signals, fire pump and electric valve signals, which are connected by human machine interface (HMI). The PLC software has strong functions and fast speed, and meets the needs of fire control logic. The man-machine interface is reliable and flexible. It is used to display firefighters

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