The feeding of combustible liquid storage tanks is all done from the bottom. Why is that?

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Are there any standard requirements for feeding at the bottom of flammable liquid storage tanks? It is common to see that such tanks are fed from the bottom – why is that? It is mainly to prevent the generation of static electricity. \"Fire Protection Design Code for Petrochemical Enterprises GB50160-2008 (2018 Edition)\” \"(Above-ground storage tanks for flammable liquids) 6.2.24 The feed pipe of the storage tank shall be connected to the lower part of the tank body\" ； If access from above is necessary, it should be extended to a distance of 200 mm from the bottom of the tank. ”The chapter in which this clause appears is “Above-ground storage tanks for flammable liquids”; unless otherwise specified, everything referred to here pertains to “above-ground storage tanks for flammable liquids”. Explanation of this clause: 6.2.24 The feed pipe for the storage tank should be connected to it from the lower part of the tank, primarily for safety reasons and to reduce losses. Flammable liquids enter the tank from the top; if no effective measures are taken, these liquids can splash. This not only increases material loss but also leads to increased friction between the liquid flow and air, generating a large amount of static electricity. When this electricity reaches a certain potential level, it can result in discharge, triggering explosions and fires. When process requirements dictate access from the top, it should be extended to the lower part of the storage tank. For individual storage tanks, such as catalytic slurry tanks, if the feed pipe is too close to the bottom of the tank, it is prone to being clogged by catalyst, so it can be raised appropriately. The above-mentioned requirements for above-ground storage tanks apply not only to such tanks but also to the loading and unloading processes. \"Fire Protection Design Code for Petrochemical Enterprises GB50160-2008 (2018 Edition)\", \"6.4.1 Vehicle loading and unloading facilities for flammable liquids shall comply with the following provisions: 1. Loading of Class A B, Class B, and Class C A liquids shall be carried out using submersible loading nozzles.\" Not only does this standard require this, but the \"Fire Protection Design Code for Fine Chemical Enterprises GB51283-2020\" also stipulates in \"5.1.2\" that when there may be air at the top, the feed pipes for containers or tanks holding flammable liquids should be connected to the lower part of such containers or tanks ； If access from above is necessary, it should be extended to a distance of 200 mm from the bottom of the container or tank. “\"Code for Design of Oil Depots GB50074-2014\", \"8.1.9 Oil unloading system for receiving railway tank cars from below.\" A sealed pipeline system should be used. When filling armored Class B, Class C, and Class A liquids into railway tank cars from above, a dip pipe inserted into the bottom of the tank car should be used. The flow velocity of the liquid inside the flexible hose should not exceed 1 m/s before the hose is submerged in the liquid, and should not exceed 4.5 m/s after it is submerged. ”8.2.8 When filling tank cars with Class B, Class C, and Class A liquids using a top-mounted loading arm, a loading arm that can reach the bottom of the tank car shall be used. The flow velocity of the liquid inside the flexible hose should not exceed 1 m/s before the hose inlet is submerged in the liquid, and should not exceed 4.5 m/s after it is submerged. \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems SH/T3007-2014\": \"5.3.13 The feed pipe of storage tanks should preferably be connected at the lower part of the tank body.\" ； The cleaning pipeline for internal floating roof tanks, as well as the pipelines for feeding combustible liquids with a temperature of 120°C or higher into the tanks, should be connected to the tanks from the tank top or the upper part of the tank body. When connecting from the top of the tank or the upper part of its body, the feed pipes for liquids of Class A, B, and C A should extend to a distance of 200 mm from the bottom of the tank, while the feed pipe for liquids of Class C B should direct the liquid toward the tank wall.