Lng Regasification Configurations and Methods

Abstract

LNG composition of LNG from a storage tank or other source is modified in a process in which the LNG is pumped to a first pressure and split into two portions. One portion of the pressurized LNG is then reduced in pressure and heavier components are separated from the reduced pressure LNG to thereby form a lean LNG. The lean LNG is then pumped to a higher pressure and combined with the other portion to form a leaner LNG. Preferably, separation is performed using a demethanizer, wherein part of the demethanizer overhead product is condensed to form the lean LNG, while another portion is used for column reflux. In further preferred configurations, ethane recovery is variable and in yet other configurations, propane or ethane can be delivered via a batching pipeline.

Description

[0001]This application claims priority to our copending U.S. provisional patent applications with Ser. Nos. 60 / 584,611, and 60 / 683,181, which were filed Jun. 30, 2004 and May 20, 2005, respectively, and which are both incorporated by reference herein.FIELD OF THE INVENTION[0002]The field of the invention is gas processing, especially as it relates to regasification of liquefied natural gas for heating value control, and recovery or extraction of C2, and C3 plus components for sales.BACKGROUND OF THE INVENTION[0003]As the demand for natural gas in the United States has risen sharply in recent years, the market price of natural gas has become increasingly volatile. Consequently, there is a renewed interest in import of liquefied natural gas (LNG) as an alternative source for natural gas. However, most import LNG has a higher heating value and is richer in heavier hydrocarbons than is allowed by typical North American natural gas pipeline specifications. For example, while some countri...

AI Technical Summary

Benefits of technology

[0011]The present invention is directed to configurations and methods of processing LNG in which the pressure of one portion of the LNG is set to a processing pressure at which LNG processing takes place to thereby generate a processed (typically lean) LNG. The so formed processed LNG may then be further pressurized to a delivery pressure and combined with a second portion of (typically unprocessed) LNG at delivery pressure to so generate LNG with a desired and predetermined chemical composition and heating value. Preferably, processing of the LNG is performed in a refluxed demethanizer that allows removal and / or recovery of at least 99% propane and over 70% ethane from the LNG.

[0018]In especially contemplated plants where ethane recovery or ethane rejection or varying levels of ethane recovery is desirable, the demethanizer bottoms can be further processed in a deethanizer column to produce a C2 overhead liquid, and a C3+ bottoms product. In this case, the deethanizer overhead reflux duty can be supplied by the refrigeration content of the inlet LNG. Ethane rejection or varying level of ethane recovery can be efficiently achieved by diverting at least a portion of the liquid ethane product from the deethanizer overhead to blend with the lean LNG. Such configuration allows the flexibility of switching between ethane recovery to ethane rejection mode or vise versa, without altering the upstream processing conditions.

Problems solved by technology

As the demand for natural gas in the United States has risen sharply in recent years, the market price of natural gas has become increasingly volatile.

One of the problems with LNG import is that a substantial fraction of the world LNG supply is rich LNG with non-compliant heating values.

California also imposes constraints on specific gas components for compressed natural gas consumption.

Currently, acceptable LNG that meets the California specification is limited to sources such as the Kenai, Alaska LNG, or the Atlantic LNG from Trinidad.

However, there are limits on the maximum amount of nitrogen and inerts that can be introduced to the pipeline gas.

Moreover, dilution with nitrogen often requires an air separation plant to produce the nitrogen, which is costly and produces no other benefit for the facility, and a lean gas source is often not available for blending in a relatively large LNG regasification facility.

However, either heating process is undesirable as fuel gas heaters generate emissions and CO2 pollutants, and seawater heaters require costly seawater systems and also negatively impact the ocean environment.

Furthermore, dilution with nitrogen to control the natural gas heating value is typically uneconomical as it generally requires a nitrogen source (e.g., an air separation plant) that is relatively costly to operate.

While the dilution methods can produce “on-spec” heating values, the effects on LNG compositions are relatively minor, and the final composition (especially with respect to C2 and C3+ components) may still be unacceptable for the environmental standards of the North America or other environmental sensitive markets.

These processes are energy inefficient when high propane and ethane recoveries are required on processing richer LNG (LNG with high ethane and propane and heavier content) for regulation compliance, because these processes would require operating the flash drum and demethanizer at an even lower pressure that would significantly increase the compression costs.

Unfortunately, the consumer markets of these liquid products are typically at a significant distance from the LNG regasification terminals, and dedicated pipeline transportation systems would have to be installed.

Additionally, the C2 or C3 market is often subject to seasonal fluctuation.

Unfortunately, most current NGL plants fail to address these operating modes, subsequently losing the potential revenue benefits from the operation from ethane recovery to ethane rejection or vise versa.

Consequently, while numerous processes and configurations for LNG regasification are known in the art, all of almost all of them suffer from one or more disadvantage.

Most notably, many of the currently known processes are energy inefficient, and inflexible in meeting the heating values and composition requirements.

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