Comparison of water fire protection system design

Comparison of water fire protection system design of chemical plants at home and abroad

Abstract: on the basis of summarizing the water fire protection design of large and medium-sized chemical plant projects invested abroad, the design of chemical water fire protection system at home and abroad is compared in the aspects of fire protection system, power supply guarantee, starting mode of water pump, form of pipe and fire water pool

key words: fire protection design of water pumps in chemical plants in recent years, many foreign multinational chemical group companies (such as Bayer, DuPont, ICI, elf ATO, Chevron, etc.) have invested in various large and medium-sized projects in China. Because most of these projects are designed by foreign design companies or insurance requirements of insurance companies, the design of water fire-fighting system generally refers to the relevant requirements of American NFPA. In terms of fire-fighting system, power supply guarantee, starting mode of water pump, form of pipe and fire pool, it is quite different from the traditional fire-fighting design of chemical enterprises in China

1 different fire-fighting system settings

China's traditional chemical plant water fire-fighting system is generally designed according to the temporary high-pressure fire-fighting water supply system, that is, the fire-fighting water tank is set on the roof of the highest building. For example, the plant water fire-fighting system includes three systems: indoor and outdoor fire hydrant system, automatic sprinkler system and foam fire-fighting system in the storage tank area. Generally, three sets of fire-fighting water pumps (one for use and one for standby) are set respectively to supply the above three systems. However, foreign engineering companies often design stable high-pressure fire water supply system or constant high-pressure fire water supply system

the so-called stable high-pressure system refers to the fire water supply system in which the pressure at the most unfavorable point in the system is usually maintained by the pressure stabilizing facilities to meet the needs of fire fighting. The system is equipped with a fire pump. When extinguishing the fire, the fire pump is started by the pressure linkage, Make the water pressure and flow at the most unfavorable point in the pipe meet the fire extinguishing requirements [1. However, there is no "stable high pressure system" in the code for fire protection design of buildings GBJ (2001) [2 Generally, the system is regarded as a temporary high-voltage system. Since chemical plants are mostly single-story or multi-storey buildings, the roof water tank can not meet the requirements of the fire water pressure at the most unfavorable point, but the stable high-pressure system can make up for this defect. The pressure of the fire pipe is maintained by the stabilized pressure pump and the stable fire pressure tank, so the stable high-pressure system does not have a roof fire water tank. Taking the indoor and outdoor fire hydrant system, automatic sprinkler system and foam fire extinguishing system in the storage tank area as an example, the stable high-pressure system can be divided into medium pressure system and high-pressure system. The medium pressure fire water supply system supplies water for indoor and outdoor fire hydrants and automatic sprinkler systems, while the high pressure fire water supply system supplies fire water for the storage tank area. The system can be composed of a stabilized pressure pump set and three fire pumps (one medium pressure fire pump, one high pressure fire pump and one standby pump). According to the pressure of the pipe, the stabilized pressure pump will automatically start or stop under the control of the pressure switch to maintain the pressure of the pipe. The standby pump is equipped according to the maximum fire water volume and maximum water pressure in the plant

the above fire protection system form is often used in today's foreign-funded projects, but some foreign-funded projects also use the constant high-pressure fire water supply system, that is, the system does not have a roof tank, and the fire pipe can also meet the flow and pressure requirements required for fire protection at the most unfavorable point at ordinary times. However, when the horizontal 2D excitation valve has two degrees of freedom for circumferential rotation and axial linear motion, the operating cost is higher than that of the stable high-pressure system

2 different requirements for power supply

according to the provisions of article 8.8.5 of the code for fire protection design of buildings, the fire pump station or pump room with standby pump should use the power of the equipment. If it is difficult to use dual power supply or dual circuit power supply, the internal combustion engine can be used as the power. However, foreign engineering companies sometimes use the internal combustion engine as the power of the standby pump even when there is dual power supply or dual circuit power supply, so as to ensure that the fire pump has a more reliable power supply. Although this increases the investment cost, the startup and operation of the fire pump are more reliable in case of fire

3 the starting methods of water pumps are different.

since the water pumps of each system are set separately, the number of "pressure supplement" depends on the material and manufacturing quality of the packaging bag. The starting of the fire hydrant pump of the temporary high-pressure fire water supply system is divided into two ways: the direct starting of the fire hydrant button and the bus starting of the fire control center

due to the combination of the system, the water pump of the stable high-pressure fire water supply system can be started automatically according to the pressure linkage of the fire pipe or the bus of the fire control center, and the fire hydrant does not need to be set with a start button. Under normal production conditions, the normal pressure of the system is maintained by the stabilized pressure pump and the stabilized pressure tank. The stabilized pressure pump automatically starts and stops under the control of the pressure switch. When the pressure of the fire pipe drops to a certain value, the stabilized pressure pump automatically starts and continues to operate until the pressure of the fire pipe reaches a certain value, and the stabilized pressure pump stops. In addition, each fire pump is equipped with an independent pressure switch. The fire pump starts automatically and in sequence. During fire fighting, when the pressure of the fire pipe decreases to the set value of the pressure switch, the fire pump will be started first. After a period of time, if the water pressure of the fire pipe continues to fall, the standby diesel fire pump will be started

in some projects, the stabilized pressure pump is normally open to achieve the pressure required by the system. In order to prevent the system from overpressure, a return pipe is set on the main outlet pipe of the water pump, which also makes the graphene products have the ability of "needle insertion and water splashing", and the water flows back to the pool through this pipe

4 differences in the laying methods of fire pipelines

most outdoor fire pipelines in domestic projects are laid underground. In foreign projects, outdoor fire pipelines are often laid on pipe racks to minimize the quantities of underground pipelines

5 different forms of fire water pools

in the design of domestic projects, fire water pools generally adopt the form of closed reinforced concrete. As the concrete pool looks bulky, especially for some large fire pools, if the above ground form is adopted, the overall beauty of the plant will be affected. Therefore, foreign engineering companies often use the form of steel water tanks for larger fire water tanks. Although the thermal insulation performance of steel water tanks is not as good as that of concrete water tanks, their appearance is lightweight, and the use of above ground forms does not affect the beauty of the plant in May 2013. Sometimes, the fire pool also adopts the open form, which is usually used as the waterscape of the plant

the above is only my experience in engineering design in cooperation with foreign engineering companies

References:

[1 dgj08-94-2001, code for design of water fire extinguishing systems in civil buildings [s

[2 GBJ 16-87, code for fire protection design of buildings [s