Method and system for pre-cooling ethylene storage tank by low temperature nitrogen

Abstract

The invention discloses a method and a system for pre-cooling an ethylene storage tank by low temperature nitrogen. The method comprises the following steps of: 1) opening a valve at the bottom of the ethylene storage tank, introducing normal-temperature nitrogen through a pipeline extending into the top of the valve, and drying; 2) meanwhile, introducing low-temperature nitrogen to the top and bottom, and pre-cooling, wherein the low-temperature nitrogen is prepared by mixing liquid nitrogen coupled to a gas-liquid separator and sub low-temperature nitrogen, and the low-temperature nitrogen is obtained by gasifying liquid nitrogen; 3) gradually cooling the low-temperature nitrogen through sub low-temperature nitrogen amount stably connected to the gas-liquid separator and liquid nitrogen amount continuously introduced to the gas-liquid separator so as to gradually cool the ethylene storage tank. The system disclosed by the invention can be used for dynamically adjusting the temperature of low-temperature nitrogen for pre-cooling the ethylene storage tank by arranging two parallel branches which are respectively used for gasifying liquid nitrogen and dynamically adjusting the flow of the liquid nitrogen, so that the temperature of low-temperature nitrogen is controllably and gradiently lowered so as to realize the expected pre-cooling effect. The method and the system are safe to use and lower in cost.

Description

technical field [0001] The invention relates to a technology for precooling a low-temperature liquid storage tank (temperature <-50° C.) by using low-temperature nitrogen, in particular to a method and system for precooling an ethylene storage tank by using low-temperature nitrogen. Background technique [0002] Pre-cooling of large cryogenic liquid ethylene storage tank means that before the storage tank is filled with cryogenic liquid for the first time, the medium with different temperature gradients is used to cool the storage tank from high temperature to low temperature until the storage tank reaches the condition of receiving low temperature liquid. Prevent stress deformation and damage caused by sudden drop in tank temperature. [0003] At present, the precooling of ethylene storage tanks is generally realized by the ethylene body. The disadvantage is that: because part of the ethylene is mixed with the gas phase and liquid phase and sent into the storage tank, th...

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Problems solved by technology

[0003] At present, the precooling of ethylene storage tanks is generally realized by the ethylene body. The disadvantage is that: because part of the ethylene is mixed with the gas phase and liquid phase and sent into the storage tank, the factors that affect the outlet temperature of the precooling device are the amount of gasification, the temperature after gasification, and The amount of liquid, these factors are difficult to control well, so the outlet temperature of the pre-cooling device is high and low, it is difficult to achieve the purpose of gradually decreasing the temperature, which affects the pre-cooling effect of the storage tank; on the other hand, the cost of using ethylene pre-cooling is also high. High (11,000 yuan / ton) and unsafe

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