Mobile liquid nitrogen fire extinguishing system and method for utility tunnel

A mobile liquid nitrogen fire extinguishing method for a utility tunnel, comprising:

• (a) when a fire occurs in a cabin of the utility tunnel, sensing a fire position by sensors at liquid nitrogen injection ports, feeding back a signal to a master control of the utility tunnel, controlling to close corresponding facilities in the utility tunnel by the master control of the utility tunnel, and sending alarm and positioning information to a controller, controlling a liquid nitrogen production assembly and a fire extinguishing assembly by the controller to move to a target location, and connecting the liquid nitrogen production assembly to the fire extinguishing assembly via a metal hose, and connecting the fire extinguishing assembly to a reserved interface of a liquid nitrogen conveying tubing through another metal hose;
• and
• starting a liquid nitrogen booster pump by the controller;
• regulating an input flow of liquid nitrogen in a liquid nitrogen storage tank by a proportional control valve;
• after regulating an output pressure by the liquid nitrogen booster pump, enabling the liquid nitrogen enters the liquid nitrogen conveying tubing and branch pipes through a flow meter and a safety valve in sequence;
• and injecting the liquid nitrogen from the liquid nitrogen injection ports on each of the branch pipes into the utility tunnel to perform a liquid nitrogen fire extinguishing inside the utility tunnel;
• (b) monitoring a pressure in the liquid nitrogen storage tank by a pressure gauge on the liquid nitrogen storage tank in real time, dividing the pressure into a filling range, a working range, and a dangerous range based on a magnitude of the pressure;
• if the pressure in the liquid nitrogen storage tank is in the filling range, starting the liquid nitrogen production assembly by the controller, such that surrounding air is extracted by an air compressor from an air inlet on a top of the air compressor for filtering and compression, and conveying the surrounding air to a nitrogen production machine for treatment, producing liquid nitrogen by a refrigeration liquefier by using nitrogen generated by the nitrogen production machine, and supplying the liquid nitrogen to the liquid nitrogen storage tank through a first metal hose;
• performing the liquid nitrogen fire extinguishing in the utility tunnel normally if the pressure is in the working range;
• and if the pressure is in the dangerous range, opening a pressure relief valve automatically, so as to discharge nitrogen gas generated after gasification of liquid nitrogen under heating, such that the pressure is recovered to the working range;
• and
• (c) controlling an automatic simultaneous operation of a liquid nitrogen preparation, a liquid nitrogen storage, and the liquid nitrogen fire extinguishing by the controller;
• after the liquid nitrogen fire extinguishing is completed, controlling the liquid nitrogen production assembly by the controller such that the liquid nitrogen production assembly stops working when the pressure in the liquid nitrogen storage tank reaches the working range after the liquid nitrogen is supplemented.