Process and system to produce multiple distributable products from source, or imported LNG

The process that includes providing the following elements for treating source refrigerated LNG, a heat exchanger/condenser through which refrigerated LNG passes, a vaporizer receiving LNG from the heat exchanger/condenser to produce heating grade LNG product, a distillation column producing distillate condensed in the heat exchanger/condenser to produce vehicle grade LNG, some of which is returned to the distillation column, the distillation column having input of refrigerated LNG, the distillation column having a lower outlet through which produced C2+ is delivered.

BACKGROUND OF THE INVENTION

This invention relates generally to treatment of import grade liquefied natural gas (LNG) for uses in addition to formation and distribution of natural gas for commercial purpose. More specifically, it concerns such treatment to form engine fuel grade LNG, and/or to produce commercially distributable gas at elevated pressure.

Liquefied natural gas (LNG) is typically transported by ship to provide fuel in areas where there is insufficient indigenous natural gas. Once unloaded from the ship, it is stored in large storage tanks and then pumped and heated prior to being injected in gaseous state into a distribution pipeline. The primary end use for the natural gas is as fuel, where the exact chemical composition is of little concern.

There is however, an alternate use for LNG as a motor vehicle fuel where the LNG is carried on the vehicle in liquid form and, after conversion to warm gas, is combusted in an engine. Engines cannot tolerate many of the compounds frequently found in raw LNG, as they cause pre-ignition. High concentrations of many compounds, such as ethane, preclude normal LNG from being used as motor fuel.

It is possible to process LNG (heating grade) into LNG (vehicle engine fuel grade) by removing the undesirable compounds. See in this regard U.S. Pat. No. 6,986,266. One characteristic of conversion methods is the requirement for refrigeration. This raises both the capital cost and operating cost.

SUMMARY OF THE INVENTION

Large LNG receiving and send-out terminals present a unique opportunity to use already available LNG refrigeration, as well as pressurization. The present invention involves use of the refrigeration of the LNG being pumped and sent out (injected into a pipeline) to provide refrigeration necessary to convert a portion of the stream into a more purified stream of LNG (vehicle grade).

The invention also concerns provision of a system or process in which the following elements are provided for treating source refrigerated LNG:

a) a heat exchanger/condenser through which refrigerated LNG passes,

b) a vaporizer receiving LNG from the heat exchanger/condenser to produce heating grade LNG product,

c) a distillation column producing distillate condensed in the heat exchanger/condenser to produce vehicle grade LNG, some of which is returned to the distillation column,

d) the distillation column receiving input of refrigerated LNG,

e) the distillation column having a lower outlet through which produced C2+ is delivered.

The system provides a simple method for producing vehicle grade LNG from imported LNG, using the refrigeration from the send out of heating grade LNG to distribution.

Additional objectives include

1) providing s secondary heater vaporizer receiving product from a lower portion of the distillation column and returning product to a lower portion of the column;

2) delivering LNG product to a pipeline grid; delivering condensed vehicle grade LNG to both the distillation column and to a storage or transport facility; and delivering C2+ product from the bottom of the distillation column to a storage or transport facility;

3) pumping a first portion of source LNG to elevated pressure level for passage to the heat exchanger/condenser for heat exchange with said distillate column produced distillate condensed in the heat exchanger/condenser to produce vehicle grade LNG, some of which is returned to the distillation column,

4) pumping a second portion of source LNG to elevated pressure for passage to the distillation column for distillation.

DETAILED DESCRIPTION

InFIG. 1, the preferred form of the invention, heating grade source LNG, supplied at10as from a ship or transport vessel, is stored at11, as imported LNG. It is desired that vehicle engine grade LNG be derived from the LNG stored at11, and supplied for commercial purposes as at12, as for example from storage at13. A commercial transport vehicle is shown at14receiving the vehicle grade LNG.

The refrigerated heating grade LNG supplied at20as from storage11is pumped by main send out pump at15for delivery at16to heat exchanger/condenser apparatus17, from which it flows at18to a vaporizer19. The pump elevates the LNG to pipeline pressure, typically 50 to 100 atmospheres; and the vaporizer operates to heat the cold LNG to warm temperature, typically 10 to 20 degrees Centigrade, for conversion to gas. The gasified LNG is then delivered at21to a commercial pipeline41, as HGLNG (heating grade LNG).

The process utilizes the “cold” containing in the LNG stream20to provide refrigeration to a distillation column26operating to purify the LNG to vehicle grade (typically 99% methane). A secondary pump40receives cold LNG stream20a, and delivers it to a mid-point41′ of column, as for example at about 7 bara. The column pressure may vary over a broad range, from about 4 bara to the critical point of methane.

The liquid LNG flowing through one side of the exchanger17is heated slightly (typically from 115 degK to 120 degK). The other side involves condensing a near pure methane gas stream21from column26at a higher than atmospheric pressure (typically 7 to 14 atm). Most of the condensed methane is delivered at28(for flow by gravity or pumping) to the top of the distillation column26as reflux.

The remainder of the condensed methane is delivered at23to VGLNG (vehicle grade LNG) storage13, from which that product is controllably delivered at12to transport vehicles14for distribution to fuel stations for vehicles.

The distillation column26has a lower outlet44, through which bottoms product such as C2+ is delivered at45to C2+ storage46, and transport at58where C2+ constitutes a liquid hydrocarbon stream containing ethane and heavier hydrocarbon components.

The C2+ product may be refined into nearly pure ethane and a C3+ bottoms hydrocarbon. As an alternative arrangement, the C2+ stream can be delivered at50for combination with the HGLNG stream at point51, for processing in vaporizer19and delivery to pipeline.

Also shown is a secondary heater vaporizer56receiving product (such as C2+) via stream57from a lower portion of the column26, for returning lighter product (such as remanent methane), and bottoms, at57to the column at58.

Accordingly, the invention provides a simpler, efficient method for producing three distributable products (HGLNG, VGLNG, C2+) from imported refrigerated LNG.