Research On Fire Simulation And Countermeasures Against Fire Protection For Natural Gas In Underground Utility Tunnel

With the acceleration of urbanization in China,in order to use of urban land resources economically,improve the efficiency of urban engineering pipelines,ease urban traffic congestion,and improve the city's civilized and visual landscape,then underground utility tunnel has emerged in the city.According to the "Technical Specification for Urban Integrated Pipeline Project" GB50838-2015,natural gas pipelines can be integrated into underground utility tunnel.However,there are no relevant documents specifically for the laws of natural gas cabin fires,and the detectors set for the natural gas space in the existing specifications are specifically designed.The selection of fire extinguishing methods and other settings are based on other specifications.Whether it is reasonable or not requires further demonstration.This project takes the natural gas pipeline in an underground in Xi'an as the research object,and uses theoretical analysis and numerical simulation methods to study the characteristics of smoke flow and temperature distribution in the chamber.Based on this,we put forward reasonable firefighting countermeasures,which are intended to put forward the relevant basis for preventing natural gas fires in underground integrated pipe corridors and ensure the safety of natural gas transport in pipeline corridors.The main research conclusions are as follows:(1)Using Fluent to conduct numerical simulations of fires in natural gas chambers,analyze and study the characteristics of the smoke flow in the chambers and the distribution of the temperature field.The results show that in the case of continuous natural gas leakage,the 200m-long closed pipeline corridor the air can only sustain the fire for about 3 minutes;the concentration and temperature of the flue gas in the natural gas chamber are all “partitioned”.The temperature of the upper flue gas near the fire source is above 2000 K,which is damage to the natural gas chamber's structure.With the accumulation of smoke at the end of the tube,the temperature of the flue gas at the end rises slightly.Therefore,the escape port of the natural gas tank should not be installed at the two ports of the tube.It is recommended to set it at 5-8 meters from the end.(2)The use of high-temperature damage to the human body and the tube compartment to divide the hazardous area in the fire-spreading area in the tube compartment.The results show that the dangerous area in the tube room expands with the increase of the fire time,when the fire occurs for 60 s,the whole of tube compartments are all dangerous and there is no safe area suitable for the human body.After natural gas leakage,when the leakage pressure is the same,the gas diffusion distance has a positive correlation with time,y=a+bx(x?1).The slope of the curve represents the diffusion rate of gas in the chamber;Using the lower explosion limit of the combustible gas to classify the gas leak zone in the chamber,the safety zone of the chamber decreases with the increase of the leak time,and the danger zone expands with the increase of the leak time,and the dangerous zone in the chamber is mainly located in leakage outlet downstream direction.(3)Based on the characteristics of smoke gas flow and the distribution of temperature field in the natural gas chamber,the fire protection measures are analyzed.The results show that it is recommend 20% of the lower explosion to be as the response concentration of alarm detector is limit under accident conditions.The gas detectors and temperature detectors shall be arranged in the chamber to jointly monitor the abnormal conditions occurring in the chambers.The dry powder is superior to the water extinguishing system in suppressing and extinguishing the fire.Therefore,dry powder spraying should be selected is better than the water extinguishing system in the natural gas chamber.