What Should Be Paid Attention To During Loading And Unloading Of Liquefied Petroleum Gas Railway Crane Pipes?

The liquefied petroleum gas railway loading and unloading crane is the main equipment for railway tank truck loading and unloading operations. There are two types of liquefied petroleum gas railway loading and unloading cranes: one is the universal unloading crane, and the other is the rubber flange unloading crane.
The universal crane pipe is composed of a riser and a universal joint. The universal joint formed by the elbow equipped with a "rolling ball" can be conveniently connected with the gas and liquid phase pipes of the tank car. The rubber hose flange crane pipe is composed of a vertical pipe, a threaded joint, a high-pressure armored oil resistant rubber hose, a flange joint, a threaded stop valve, and a loop flange.
The liquefied petroleum gas railway loading and unloading bridge is an operating platform set up for loading and unloading operations. It is generally built together with a crane pipe, and there is a lifting ladder (with a tilt angle of no more than 60 °) between the bridge and the tank car, from which operators can climb up to the tank car for operation.
The loading and unloading method of liquefied petroleum gas railway tanker mainly depends on the terrain conditions of the liquefied petroleum gas warehouse and the structural form of the tanker.
(1) Self flow loading and pumping loading are mainly carried out by utilizing the high altitude difference of the terrain for self flow loading. This loading method not only saves investment and reduces costs, but also is not affected by power supply, safe and reliable. However, it requires the terrain conditions for self flow loading. Pumping loading is a method used when terrain conditions for gravity loading are not available. At present, many reserve oil depots in China are built in mountainous areas, and storage areas are mostly arranged in the depth of mountains or canyons, with most of the elevation higher than the elevation of the operating area. So, most oil depots use pump unloading and gravity loading.
(2) Upper unloading: The upper unloading mainly involves inserting the rubber hose or movable aluminum tube at the end of the crane tube into the tank car cover on the upper part of the liquid tank car, and then using a pump or siphon to unload the car. When using a railway tank car to fill armor or Class B liquid from the top, a crane pipe inserted into the bottom of the tank car should be used. The flow velocity of the liquid inside the crane tube should not exceed 4.5m/s. When using a pump to unload liquid, it is necessary to ensure that the pump suction system is filled with liquid and there is no air blockage or flow interruption at the top of the crane pipe or any part of the suction system. Therefore, a vacuum pump must be equipped to meet the requirements of filling and pumping bottom liquid oil. Its characteristic is that the liquid discharged from the bottom of the tanker can be directly pumped to the liquid storage tank without passing through the zero position tank, reducing the evaporation of liquefied petroleum gas. However, tall crane pipes, trestles, and vacuum systems need to be installed; There are many equipment, complex operations, and a high risk of fire, which also forms an air lock and affects normal oil unloading.
In order to prevent the high-pressure armored oil resistant hose from breaking or breaking, the allowable working pressure is at least 4 times the maximum working pressure of the system. Generally, high-pressure armored oil resistant hose with steel wire is selected, and the length is usually around 4m. For ease of operation, the unloading crane tube of the rubber hose flange is fixed on a specialized hanger. With the help of the crane tube hanger, the relative position of the flange joint and the railway tank car can be changed while aligning. The structural dimensions and installation position of the loading and unloading crane tube itself must comply with the relevant provisions of the "Standard Gauge Railway Building Approach Gauge". The horizontal extension distance of the crane tube must not be less than 2 or 6 meters, otherwise it cannot extend into the loading and unloading port inside the tank car. The height difference between the lowest position of the non detachable part of the crane pipe extending to the tank car end and the rail top shall not be less than 5 or 5 meters. To prevent static electricity or stray current discharge from detonating, the crane tube is equipped with a grounding device. The structural form of the crane tube requires easy operation, no air leakage, good sealing, and safety and reliability.
(1) When the loading and unloading operation line of liquefied petroleum gas and the loading and unloading operation line of Class C and B liquids are combined and operated simultaneously, the distance between the two types of cranes should not be less than 24m; When working at different times, the distance between the two types of cranes can be unrestricted.
(2) The center line of the large crane pipes arranged on both sides of the two dedicated lines with a walking distance of ± 2m should be 2.6m from the center of the railway dedicated line, and the distance between adjacent crane pipes should be 12m. The distance between the loading and unloading crane pipe and the fence and railway gate should not be less than 20m.
(3) In the railway loading and unloading area for combustible liquids, the distance between the diesel locomotive and the crane pipe of another stack should not be less than 12m for Class A and B liquids, and not less than 8m for Class C liquids. The distance between the two adjacent stack cranes should not be less than 10m, but the distance between the two adjacent stack cranes for loading and unloading Class C liquids should not be less than 7m. When combustible liquids are loaded and unloaded in a sealed manner, their fire prevention distance can be reduced by 25%.
It is best to control the loading flow rate within 4.5m/s, as the liquid phase port of the liquefied gas crane pipe only has DN50, a loading flow rate of 30m3/h is more suitable. If the loading time allows, it is best for liquefied gas to be less than 3m/s.
When the liquid level of the tank truck is higher than the zero level tank and there is sufficient liquid level difference, siphon self flow unloading can be used. But it is necessary to have equipment for vacuuming or filling liquid to fill the crane pipe siphon. The main advantages of this oil unloading method are fewer equipment and simple operation; The disadvantage is the addition of zero position oil tanks, additional transmission, and increased evaporation of liquefied petroleum gas. The use of immersion oil pumps for upper unloading of oil products has also been used. This submerged oil pump system is installed at the end of the hose of the unloading crane pipe. The pump is driven by an electric motor, which is installed together in a sealed casing. The motor is cooled by the transported oil. This oil unloading method is flexible and effective, mainly suitable for outdoor operations, but the motor must ensure the explosion-proof level requirements.