Method for reducing dew point of refrigerant pipeline of cryogenic device of LNG (Liquefied Natural Gas) ship

Abstract

The invention discloses a method for reducing the dew point of a refrigerant pipeline of a cryogenic device of an LNG (Liquefied Natural Gas) ship, which specifically comprises the following steps of: S1, connecting an outlet valve of a marine nitrogen pipeline with an inlet valve of the refrigerant pipeline of the cryogenic device through a metal hose, and communicating the outlet valve of the refrigerant pipeline with outdoor atmosphere by using the metal hose; s2, first-stage purging is conducted on the refrigerant pipeline, and nitrogen purging is conducted on the refrigerant pipeline; s3, measuring the gas dew point of an outlet valve of the refrigerant pipeline every four hours; s4, second-stage purging of the refrigerant pipeline is carried out, the refrigerant pipeline is purged through a bin sweeping pipe connector after wharf liquid nitrogen is gasified, the dew point of the refrigerant pipeline is measured, and the oxygen content of the refrigerant pipeline is detected through an oxygen content detector; and S5, the step S3 is repeated, the sensor instrument pipe on the refrigerant pipeline is purged, and the refrigerant pipeline purging work is completed. According to the invention, through two-stage purging of the refrigerant pipeline and multiple times of pressure boosting and pressure reducing, the problem of incomplete purging of the refrigerant pipeline due to complex trend of the refrigerant pipeline is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of shipbuilding, and particularly relates to a method for reducing the dew point of the refrigerant pipeline of an LNG ship cryogenic device. Background Art

[0002] LNG ships are known as the "pearl on the crown of shipbuilding", and the ultra-low temperature cargo operating system has always been the main focus and difficulty in their construction. During ship operation, a cryogenic device is used to control the cargo hold temperature. The cryogenic device compresses the refrigerant medium using two MCMs (compressors), and then expands the refrigerant through an MTC (compression expander), thereby reducing the refrigerant temperature to -175°C. Through heat exchange, the liquid LNG is further cooled, so as to achieve the purpose of deep cooling of the liquid LNG, realize the control of the cargo hold pressure, and reduce the evaporation amount of the cargo hold. Since the working temperature of the refrigerant is around -175°C, if there is water vapor in the refrigerant pipeline, the water vapor will freeze at low temperatures, which will cause fatal damage to the impellers of the high-speed rotating equipment. Therefore, whether the dew point in the refrigerant pipeline meets the requirements is related to the normal operation of the equipment. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies existing in the above-mentioned prior art, and provide a method for reducing the dew point of the refrigerant pipeline of an LNG ship cryogenic device. The present invention completes the purging of the refrigerant pipeline through purging in two stages of the refrigerant pipeline, and at the same time, through multiple pressure increases and decreases, it avoids the problem of incomplete purging of the refrigerant pipeline due to the complex routing of the refrigerant pipeline, and improves the purging efficiency of the refrigerant pipeline.

[0004] In order to achieve the above-mentioned invention purpose, the technical solution provided by the present invention for the patent is as follows:

[0005] A method for reducing the dew point of the refrigerant pipeline of an LNG ship cryogenic device, the method specifically includes the following steps:

[0006] S1, after the cryogenic device is installed on the LNG ship, connect the outlet valve of the marine nitrogen pipeline with the inlet valve of the refrigerant pipeline of the cryogenic device through a metal hose, and use the metal hose to connect the outlet valve of the refrigerant pipeline with the outdoor atmosphere;

[0007] S2, purging in the first stage of the refrigerant pipeline, open the marine nitrogen outlet valve, the inlet valve of the refrigerant pipeline and the outlet valve of the refrigerant pipeline, and the nitrogen generated by the nitrogen generator enters the refrigerant pipeline through the metal hose from the inlet valve of the refrigerant pipeline and purges the refrigerant pipeline with nitrogen;

[0008] S3. Measure the gas dew point of the refrigerant pipeline outlet valve every 4 hours. When the gas dew point is lower than -50°C, open the drain outlet of the sensor instrument needle valve on the refrigerant pipeline to purge the sensor instrument pipe. Measure the gas dew point of the sensor instrument pipe every 4 hours. When the gas dew point measured by the sensor instrument pipe is lower than -40°C, close the drain outlet of the sensor instrument pipe to complete the purging of the sensor instrument pipe.

[0009] S4. Second-stage purging of the refrigerant pipeline: Connect the refrigerant pipeline inlet valve to the tank cleaning pipe interface through a metal hose. After the terminal liquid nitrogen vaporizes, it purges the refrigerant pipeline through the tank cleaning pipe interface. Measure the dew point of the refrigerant pipeline every 2 hours. When the dew point of the refrigerant pipeline is lower than -50°C, use an oxygen content detector to detect the oxygen content of the refrigerant pipeline.

[0010] S5. Repeat step S3 to perform the second-stage purging of the sensor instrument pipe on the refrigerant pipeline and detect the oxygen content of the sensor instrument pipe to complete the purging work of the refrigerant pipeline.

[0011] Further, the dew point of the nitrogen generated by the nitrogen generator is -80°C, and the oxygen content is 1%.

[0012] Further, the oxygen content in the terminal liquid nitrogen is 0. The second-stage purging of the refrigerant pipeline is specifically as follows: Open the nitrogen pipeline outlet valve and the refrigerant pipeline inlet valve. The vaporized nitrogen is introduced into the refrigerant pipeline, and the pressure value inside the refrigerant pipeline is measured. When the pressure of the refrigerant pipeline is greater than 1 bar, open the refrigerant pipeline outlet valve, and the nitrogen purges the refrigerant pipeline. Measure the dew point of the refrigerant pipeline every 2 hours, and then use an oxygen content measuring instrument to measure the oxygen content of the refrigerant pipeline. When the oxygen content in the refrigerant pipeline is 0, the purging of the refrigerant pipeline is completed.

[0013] Further, after the purging of the sensor instrument pipe on the refrigerant pipeline is completed, close the refrigerant pipeline outlet valve and close all the sensor needle valve outlets on the refrigerant pipeline. When the pressure of the refrigerant pipeline rises to 6 bar, measure the dew point at the sensor outlet on the refrigerant pipeline. When the dew point at the sensor outlet is not lower than -50°C, close the refrigerant pipeline inlet valve. When the pressure of the refrigerant pipeline drops to 1 bar, measure the dew point at the sensor outlet again, and repeat the above steps until the dew point at the sensor outlet is lower than -50°C.

[0014] Based on the above technical solutions, the following technical advantages have been achieved through practical application of the method for reducing the dew point of the refrigerant pipeline of a cryogenic device on an LNG ship in this invention patent:

[0015] 1. A method for reducing the dew point of the refrigerant pipeline of an LNG ship cryogenic device of the present invention completes the purging of the refrigerant pipeline through purging in two stages of the refrigerant pipeline. At the same time, through multiple pressure increases and decreases, it avoids the problem of incomplete purging of the refrigerant pipeline due to the complex routing of the refrigerant pipeline, and improves the purging efficiency of the refrigerant pipeline. Detailed implementation manner

[0016] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be described through specific examples below. However, it should be understood that these descriptions are exemplary and do not limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0017] The present invention belongs to a method for reducing the dew point of the refrigerant pipeline of an LNG ship cryogenic device. The method specifically includes the following steps:

[0018] S1. After the cryogenic device is installed on the LNG ship, connect the outlet valve of the marine nitrogen pipeline to the inlet valve of the refrigerant pipeline of the cryogenic device through a metal hose, and use the metal hose to connect the outlet valve of the refrigerant pipeline to the outdoor atmosphere;

[0019] S2. The first-stage purging of the refrigerant pipeline: Open the marine nitrogen outlet valve, the refrigerant pipeline inlet valve and the refrigerant pipeline outlet valve. The nitrogen generated by the nitrogen generator enters the refrigerant pipeline through the metal hose from the refrigerant pipeline inlet valve and purges the refrigerant pipeline with nitrogen;

[0020] S3. Measure the gas dew point of the refrigerant pipeline outlet valve every 4 hours. When the gas dew point is lower than -50°C, open the drain outlet of the sensor instrument needle valve on the refrigerant pipeline to purge the sensor instrument pipe. Measure the gas dew point of the sensor instrument pipe every 4 hours. When the gas dew point measured by the sensor instrument pipe is lower than -40°C, close the drain outlet of the sensor instrument pipe to complete the purging of the sensor instrument pipe;

[0021] There are multiple sensor instrument pipes on the refrigerant pipeline. When purging the sensors, it is carried out in batches. In this embodiment, there are 25 sensor instrument pipes on the refrigerant pipeline, which are divided into three batches for purging, with the quantities being 8, 8, and 9 respectively. Measure the dew point of the instrument pipe every 4 hours. When the dew point reaches -40°C, stop purging this batch of instrument pipes and proceed to purge the dew point of the next batch of sensor instrument pipes;

[0022] S4. The second-stage purging of the refrigerant pipeline: Connect the refrigerant pipeline inlet valve to the tank cleaning pipe interface through a metal hose, and purge the refrigerant pipeline with the liquefied nitrogen at the terminal after gasification through the tank cleaning pipe interface. Measure the dew point of the refrigerant pipeline every 2 hours. When the dew point of the refrigerant pipeline is lower than -50°C, use an oxygen content detector to detect the oxygen content of the refrigerant pipeline;

[0023] In step S5, repeat step S3 to conduct the second-stage purging of the sensor instrument pipes on the refrigerant pipeline, and conduct oxygen content detection on the sensor instrument pipes to complete the purging work of the refrigerant pipeline.

[0024] When conducting the second-stage purging of the sensors on the refrigerant pipeline, close the outlet valve of the refrigerant pipeline and the outlet of the sensor needle valves on all refrigerant pipelines. When the pressure of the main refrigerant pipeline rises to 6 bar, measure the dew point at the outlet of the first batch of sensors. If it is not lower than -50 °C, close the inlet valve of the refrigerant pipeline, reduce the pressure of the main refrigerant pipeline to 1 bar, close the outlet of the first batch of sensor needle valves, open the inlet valve of the refrigerant pipeline, raise the pressure of the main refrigerant pipeline to 6 bar again, and measure the dew point at the outlet of the first batch of sensors. Repeat the above operations until the dew points of all points of the first batch of sensors are lower than -50 °C. Then conduct dew point purging on the sensor instrument pipes of the next batch until the dew points of all sensor instrument pipes are lower than -50 °C.

[0025] The dew point of the nitrogen generated by the nitrogen generator is -80 °C, and the oxygen content is 1%.

[0026] The oxygen content in the dock liquid nitrogen is 0. The second-stage purging of the refrigerant pipeline is specifically as follows: Open the outlet valve of the nitrogen pipeline and the inlet valve of the refrigerant pipeline. The vaporized nitrogen is introduced into the refrigerant pipeline, and the pressure value inside the refrigerant pipeline is measured. When the pressure of the refrigerant pipeline is greater than 1 bar, open the outlet valve of the refrigerant pipeline, and the nitrogen purges the refrigerant pipeline. Every 2 hours, measure the dew point of the refrigerant pipeline, and then use an oxygen content measuring instrument to measure the oxygen content of the refrigerant pipeline. When the oxygen content in the refrigerant pipeline is 0, the purging of the refrigerant pipeline is completed.

[0027] After the purging of the sensor instrument pipes on the refrigerant pipeline is completed, close the outlet valve of the refrigerant pipeline and the outlet of the sensor needle valves on all refrigerant pipelines. When the pressure of the refrigerant pipeline rises to 6 bar, measure the dew point at the outlet of the sensors on the refrigerant pipeline. When the dew point at the sensor outlet is not lower than -50 °C, close the inlet valve of the refrigerant pipeline. When the pressure of the refrigerant pipeline drops to 1 bar, measure the dew point at the sensor outlet again. Repeat the above steps until the dew point at the sensor outlet is lower than -50 °C.

[0028] After the two dew point reduction operations are completed, use the method of boosting the pressure of the refrigerant pipeline of the cryogenic device to fully mix the gas in the area where gas flow is not easily achieved in the pipeline with pure nitrogen, and then discharge the mixed gas through pressure reduction. Repeat 2 - 3 times to make the dew points of all measurement points lower than -50 °C.

[0029] Method for reducing dew point of refrigerant pipeline in cryogenic unit. The main core is that in the first stage, nitrogen with low dew point (-80°C or so) and containing oxygen (oxygen content about 1%) on the ship is used for purging the pipeline in the first stage, which can dry the refrigerant pipeline relatively quickly; in the second stage, considering the large consumption of pure nitrogen, pure nitrogen (dew point -60°C or so) after vaporization of liquid nitrogen at the dock (vaporization ratio 1:600) is used, and it is connected to the pipeline on the ship through a temporary pipeline at the dock to replace the oxygen-containing nitrogen in the main refrigerant pipeline; due to the complex routing of the refrigerant pipeline, there will inevitably be some areas where gas flow is difficult, and it is not enough to rely only on gas flow for purging. Therefore, by operating the main refrigerant pipeline to increase and decrease pressure multiple times, the gas inside the main refrigerant pipeline is fully mixed, so as to achieve that the gas dew point at all positions of the main refrigerant pipeline meets the requirements.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that it is still possible to modify the specific implementation manners of the invention or perform equivalent substitution on some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered by the scope of the technical solutions claimed in the present invention.

Claims

1. A method for reducing the dew point of a refrigerant pipeline of a LNG ship cryogenic device, characterized in that: The method specifically comprises the following steps: S1, after the cryogenic device is installed on the LNG ship, the outlet valve of the marine nitrogen pipeline is connected to the inlet valve of the refrigerant pipeline of the cryogenic device through a metal hose, and the outlet valve of the refrigerant pipeline is connected to the outdoor atmosphere using the metal hose; S2, the first stage of purge of the refrigerant pipeline, open the marine nitrogen outlet valve, the refrigerant pipeline inlet valve and the refrigerant pipeline outlet valve, the nitrogen generated by the nitrogen generator enters the refrigerant pipeline from the refrigerant pipeline inlet valve through the metal hose and purges the refrigerant pipeline with nitrogen; S3, measure the gas dew point of the refrigerant pipeline outlet valve every 4 hours. When the gas dew point is lower than -50℃, open the sensor instrument needle valve outlet on the refrigerant pipeline to purge the sensor instrument tube. Measure the gas dew point of the sensor instrument tube every 4 hours. When the gas dew point measured by the sensor instrument tube is lower than -40℃, close the sensor instrument tube outlet to complete the purge of the sensor instrument tube. S4, the second stage of purge of the refrigerant pipeline, the refrigerant pipeline inlet valve is transferred to the sweeping pipe interface through a metal hose, and the liquid nitrogen at the dock is gasified to purge the refrigerant pipeline through the sweeping pipe interface. The dew point of the refrigerant pipeline is measured every 2 hours. When the dew point of the refrigerant pipeline is lower than -50℃, the oxygen content of the refrigerant pipeline is detected using an oxygen content detector; S5, repeating step S3, performing a second stage of purging the sensor instrument tube on the refrigerant pipeline, and detecting the oxygen content of the sensor instrument tube to complete the purging of the refrigerant pipeline.

2. The method for lowering the dew point of a refrigerant pipeline of a LNG ship cryogenic device according to claim 1, characterized in that: The nitrogen generated by the nitrogen generator has a dew point of -80°C and an oxygen content of 1%.

3. The method for lowering the dew point of a refrigerant pipeline of a LNG ship cryogenic device according to claim 1, characterized in that: The oxygen content in the liquid nitrogen at the dock is 0. The second stage of purging the refrigerant pipeline is specifically as follows: open the nitrogen pipeline outlet valve and the refrigerant pipeline inlet valve, allow the gasified nitrogen to enter the refrigerant pipeline, and measure the pressure value in the refrigerant pipeline. When the refrigerant pipeline pressure is greater than 1 bar, open the refrigerant pipeline outlet valve, and purge the refrigerant pipeline with nitrogen. Measure the dew point of the refrigerant pipeline every 2 hours, and then use an oxygen content meter to measure the oxygen content of the refrigerant pipeline. When the oxygen content in the refrigerant pipeline is 0, the purging of the refrigerant pipeline is completed.

4. The method for lowering the dew point of a refrigerant pipeline of a LNG ship cryogenic device according to claim 1, characterized in that: After the sensor instrument tube on the refrigerant pipeline is purged, close the refrigerant pipeline outlet valve, close the sensor needle valve outlets on all refrigerant pipelines, and when the refrigerant pipeline pressure rises to 6 bar, measure the sensor outlet dew point on the refrigerant pipeline. When the sensor outlet dew point is not lower than -50°C, close the refrigerant pipeline inlet valve. When the refrigerant pipeline pressure drops to 1 bar, measure the sensor outlet dew point again, and repeat the above steps until the sensor outlet dew point is lower than -50°C.