Nitrogen purging method for large-sized low-temperature liquid hydrocarbon storage tank

Abstract

The invention discloses a nitrogen purging method for a large-sized low-temperature liquid hydrocarbon storage tank, which comprises the following steps that when the dew point of gas in the inner tank, the annular space and the dome of the storage tank is smaller than zero DEG C, a pressure safety valve at the top of the storage tank is kept in an online state, nitrogen is continuously fed through an inner tank replacement pipe and an annular space replacement pipe, and an emptying valve at the top of the tank is discontinuously opened and closed at the same time to conduct suppressed pressure replacement of air in the storage tank; when the volume content of oxygen in the gas exhausted from the top of the tank is smaller than 2 percent and the dew point is smaller than negative 20 DEG C, the emptying valve at the top of the tank is closed and an annular space emptying valve is discontinuously opened and closed to conduct nitrogen replacement of air in the annular space; when the measured volume content of the oxygen in the annular space is smaller than 2 percent and the dew point is smaller than negative 10 DEG C, the annular space emptying valve is closed, the nitrogen is continuously fed and the flow of the nitrogen is controlled; and when the pressure of the storage tank is increased to a high-pressure set value, nitrogen replacement of air in a process pipeline which is connected with a tank body is conducted.

Description

technical field [0001] The invention relates to the field of chemical production, in particular to a nitrogen purging method for a large-scale low-temperature liquid hydrocarbon storage tank. Background technique [0002] Large-scale cryogenic liquid hydrocarbon storage tanks usually refer to a single tank with a liquid storage capacity greater than 10,000m 3 This patent mainly relates to a large-scale flat-bottomed cylindrical low-temperature slightly positive pressure storage tank built on site for storing liquid hydrocarbons. Low-temperature micro-positive pressure liquid hydrocarbon storage tanks can be divided into single-containment tanks, double-containment tanks, and full-containment tanks according to the structural form. They are all double-layer tanks composed of an inner tank and an outer tank, and the inner and outer tanks are filled with insulating materials. [0003] After the construction of large-scale cryogenic liquid hydrocarbon storage tanks is completed...

AI Technical Summary

Problems solved by technology

[0005] The nitrogen replacement method of existing large storage tanks usually uses nitrogen to continuously inject nitrogen into the inner tank and annulus space, and continuously discharge it to the atmosphere, which basically belongs to normal pressure replacement. This method uses a very large amount of nitrogen, and it is time-consuming and costly. At the same time, the local corners of the inner tank and the annular space are not easy to be replaced to meet the standard

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