Feed letdown valve for LNG
Publication Date: 2011-Nov-30
The IP.com Prior Art Database
Natural gas (NG) is typically liquefied in a heat exchanger or a series of heat exchangers by indirect cooling with a suitable refrigerant or series of refrigerants such as gaseous nitrogen, light hydrocarbons, or mixtures of refrigerant (MR). The liquefaction process is isobaric if neglecting pressure drop across the exchanger.
Fig. 1 shows the proposed configuration using a single 2-bundle main cryogenic heat exchanger (MCHE) as an example.
A feed letdown valve (LV) is added to the feed circuit between the warm or middle bundle (WB) and the cold (CB) bundle to reduce the pressure of the LNG entering the cold bundle of the exchanger. The pressure at the inlet to the cold bundle is sufficient to deliver LNG to a storage tank (not shown). A lower pressure at the outlet of the cold bundle warms the exchanger outlet temperature while achieving the same conditions in the LNG storage tank or LNG Flash Drum (not shown). This is a result of the shape of the isotherms in the sub-cooled region in a P-H diagram. The feed letdown valve can be used in any type of heat exchanger, or a series of heat exchangers, in which the LNG entering the letdown valve would be at a temperature cold enough to produce single-phase liquid stream when reduced in pressure.