The gas stream compressed by BOG compressor is sent to the recondensing column to be absorbed by the liquid LNG stream coming from LP Pumps installed inside the storage tanks: such operation is possible due to the subcooling induced in the LNG stream by pumping action.
Part of the incoming liquid stream is diverted to the column top where an internal distributor supplies the required flowrate for condensation directly on top of a random packed section, which provides the surface required for heat exchange and mass transfer between the two phases. Liquid flow rate to the packed section is controlled by a pressure controller on the recondenser.
The BOG stream is instead introduced into the column under the packed section, to be condensed by the LNG stream described above: rising through the packing in counter-current to the descending liquid maximizes the temperature difference. The LNG Booster Pumps sumps vent line is routed back to the column to be recondensed too.
The remaining part of incoming LNG stream is diverted to the hold-up section of the column, under level control: this section ensures the required residence time and enough NPSHa for LNG Booster Pumps, also receiving the minimum flow recirculation line of these pumps.
The recondenser is provided with a padding gas entry. If the padding gas is taken downstream, the vaporizers send out line upstream of the metering station: this connection allows for maintaining the recondenser pressure at a minimum value in case the BOG compressors flow is reduced.
The recondenser is provided also with a direct controlled venting connection back to the tank vapor header: this prevents eventually excessive pressurization of the recondenser releasing gas back to the vapor header.
In case of temporary unavailability of the recondenser due to maintenance, the unit can be completely bypassed allowing to maintain the full send-out flowrate.