Seeking assistance with cooling down the cryogenic tank for the LNG project
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When starting up a cryogenic tank, a refrigeration unit should be used to supply cooling capacity in order to control the rate of temperature reduction. But in the heat exchanger of the cryogenic tank, how should the channels for the feed gas be adjusted? Should a plate-fin heat exchanger ensure that gas flows through each channel? The refrigerant channels can have the refrigerant supplied by the refrigeration unit; so how should the feed gas channels be managed during the cooling process? I would appreciate some guidance from everyone
The feed gas side is pressurized to the operating pressure, and the throttle valve is set to a slight opening; if the temperature drops too rapidly during the cooling process, it can be opened slightly more
Does it mean that maintaining a low-flow rate in the channel of the raw gas is what’s intended? So the raw gas has to be burned in a flare, right?
The raw material gas stream flows at a low volume, while the coolant flow path gradually increases its load based on the rate of cooling. The gas flow in each path contributes to the cooling process. The volume of gas in the raw material gas stream is 1/6 to 1/7 of the maximum volume; this gas is released from the hydrogen- and nitrogen-rich streams at the top of the dehydrogenation and decarburization towers, as well as from the waste streams before LNG is discharged, and it is then burned in a flare.
On the refrigerant side, the cooling rate is controlled by the throttle valve, while on the feed gas side, the overall cooling rate is adjusted by the opening degree of the product valve. The cooling rate must comply with the requirements specified in the equipment design; any excess heat can be vented through the vent valve located before the product valve and burned off in a flare. If it is possible to recover this heat, it should be done so, in order to ensure a steady cooling process within the cold box. The valves should not be opened or closed excessively, and the temperature differences at various heights within the cold box should remain within the limits allowed by the equipment, to prevent deformation, leakage, or damage to the equipment.
I carefully examined our process flow, and found that no return pipeline for the feed gas has been designed; the feed gas can only flow through the drainage from the LNG product or via the safety valve bypass