Pre-cooling of LNG pipelines before operation
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Before feeding into the LNG pipeline, it is pre-cooled using cryogenic nitrogen, which is obtained by vaporizing liquid nitrogen through an air-cooled vaporizer. I consulted manufacturers of carburetors available on the market, and all of them supply nitrogen at room temperature; none are capable of supplying nitrogen at low temperatures. May I ask the experts where I can find a vaporizer that can produce nitrogen at a low temperature of -160℃?
Thank you! Is it the nitrogen directly from the liquid nitrogen tank truck that is used? Will the traffic volume be sufficient?
By using a liquid-phase bypass, is it by injecting a small amount of liquid nitrogen into the nitrogen at room temperature to maintain its temperature?
Pre-cooling is done because the temperature of liquid nitrogen is sufficient and relatively safe. The main purpose is to cool the pipelines and tighten the connections before LNG is put into use, in order to prevent leakage accidents that could occur due to the sudden cooling of pipelines at normal temperatures. So, generally, there is no attempt to increase flow rates; instead, pre-cooling is done using tank trucks. When an optional storage tank is available, liquid nitrogen is introduced into the tank for use.
1. The safest approach: first use the tank truck’s own pressure to increase the pressure, and then pre-cool with the low-temperature nitrogen inside the tank truck. Once the pipeline was pre-cooled to -80~-100°C, it was directly pre-cooled with liquid nitrogen. 2. A more delicate approach: pre-cool directly with liquid nitrogen, using as low a flow rate as possible. This requires a high level of skill in operation; without experience, it may lead to a sudden increase in low-temperature stress on the pipes, as well as a risk of pipe supports slipping and pipes deforming