Selection of optimal schemes for the inerting process of cargo tanks of gas carriers

Recommendations are given for choosing the optimal schemes for the process of inerting cargo tanks of ships carrying liquefied gases. It was determined that one of the tasks that arise during the transportation of hydrocarbon cargoes (crude oil, petroleum products, and liquefied gases) is to ensure fire safety and prevent accidental explosions of cargo vapors in cargo tanks. Processes that occur during cargo operations on ships transporting oil products and liquefied gases are considered. The critical composition of the mixture of oxygen (entering the cargo tanks with air) and cargo vapors (remaining in the tanks after the cargo is unloaded) is indicated, at which a flash and explosion may occur. It was determined that the main technological operation that prevents spontaneous ignition of cargo vapors in cargo tanks is their inerting using nitrogen. The main advantages and disadvantages of the schemes for inerting cargo tanks are considered and determined: cascade, semi-cascade and parallel. The effective use of these schemes is based on the consumption of nitrogen, the amount of which is necessary for inerting, as well as the duration of the inerting process. The results of determining these indicators for a group of gas carriers with a cargo capacity of 38,646–62,233 m3 are given. At the same time, it is stated that the lowest consumption of nitrogen is necessary to ensure the process of inerting according to the cascade scheme. It was established that semi-cascade and parallel inerting schemes require an increase in the amount of nitrogen by 1.74–2.42 times and by 1.28–1.83 times, respectively. It was also established that the cascade scheme of inerting requires more time for its implementation. The duration of inerting according to the semi-cascade and parallel scheme is reduced and is 0.43–0.64 and 0.58–0.75 times in comparison with the cascade scheme.