Fire Risk Assessment Of Flammable Refrigerants Leakage Based On R290 And R717

The use of refrigerants has an important impact on environmental changes.With the intensification of global extreme climate and the increasing greenhouse effect,the use of more environmentally friendly refrigerants has become a research hotspot at present.Judging from the current research,the ideal refrigerant has not been found yet.In order to meet the requirements of better thermal performance and ensure the environmental protection of refrigerants,natural refrigerants such as R290,R600 a,etc.have become the primary choice for alternative refrigerants,but the disadvantage is that there is a risk of flammability.There is a risk of leakage in the process of refrigeration system operation.Once the refrigeration system leakage happened,the refrigeration system filled with combustible working refrigerants would reach a certain leakage concentration range.Where the refrigeration system is filled with flammable refrigerant,once the leakage occurs,and the concentration reaches the lower limit of combustion,there is a risk of fire accident if there are ignition sources around.Therefore,it is of great significance to study the probability of leakage fire risk in refrigeration systems filled with flammable refrigerant.Based on the actual factory leakage statistics,this paper establishes the leakage fault tree by using the fault tree analysis method,compares the leakage positions of different air-conditioning systems and the main factors causing leakage,and puts forward that the improvement of air-conditioning system leakage should focus on the bell mouth,condenser,four-way valve and two-way valve of the refrigeration system.At the same time,the common types of ignition sources are analyzed by fault tree,and the ignition probability values of different air conditioning systems are calculated.On the basis of the existing risk probability formula,considering the practical factors such as the height of obstacles in the flammable area,the distance between obstacles and leakage point,and the ratio of flammable area to the whole leakage time,the formula is modified.The revised formula is used to calculate R290 and R717,and the accuracy of the revised probability calculation value in instantaneous leakage is improved by 0.88% and 8.25%,respectively.In continuous leakage,due to the influence of the specific leakage space,the revised calculation result decreases slightly when it is in a large space,and vice versa.The leakage points of the ammonia refrigeration system are mostly located in the high temperature and high-pressure parts of the system,such as compressor,high pressure circulating liquid storage barrel(storage tank),ammonia pump,high-pressure pipeline,etc.Because the key point of ammonia danger lies in its toxicity,the main factors affecting ammonia leakage and diffusion are analyzed,and the influences of pressure,size,and shape of leakage aperture on ammonia refrigeration system leakage are obtained.The dynamic process of ammonia system leakage is programmed and calculated by Matlab,and the dynamic characteristics of leakage mass flow rate decreasing with time increase and the concentration distribution of ammonia leakage diffusion at different times are obtained.The danger of R290 mainly lies in the CO produced during combustion.Based on the existing test bench parameters,this paper simulates and verifies the CO produced by R290 combustion with Pyrosim software,and the simulation results are in good agreement with the experimental results.On the basis of this model,the curves of CO produced by combustion with different leakage flow rates of R290 were simulated.