Hydrate Formation For Gas Separation

CATEGORY: SEPARATION
PATENT
Hydrate Formation For Gas Separation
United States Patent Application 20120047944
Inventors:
Waycuilis, John J. (Cypress, TX, US)
Application Number: 13/292197
Publication Date: 03/01/2012
Assignee: MARATHON OIL COMPANY (Houston, TX, US)
Abstract:
A gas separation or gas transportation process forms a gas hydrate from an aqueous feed and a gas feed having a hydrate P-T stability envelope. While in the presence of the aqueous feed, the gas feed is initially pressurized to an operating pressure and cooled to an operating temperature which are inside the hydrate P-T stability envelope to form a gas hydrate from at least a portion of the gas feed and at least a portion of the aqueous feed. The resulting gas hydrate is readily separable from any remaining gas and stable for transport.
TECHNICAL FIELD
The present invention relates generally to gas hydrate formation processes which facilitate separation of gases in a mixture or the transportation of a gas and, more particularly, to process for forming gas hydrates in a fluidized bed heat exchanger.
BACKGROUND OF THE INVENTION
There are many hydrocarbon processing applications where it is desirable to separate higher molecular weight gases from lower molecular weight gases within a gas mixture. For example, it is common to process natural gas by separating hydrogen sulfide, carbon dioxide and/or propane from methane in the natural gas. It is likewise common to process a synthesis gas by separating carbon dioxide from more desirable hydrogen and carbon monoxide in the synthesis gas.
Processes for separating a higher molecular weight gas component from a gas mixture containing a lower molecular weight gas component and the higher molecular weight gas component often exploit differences between the boiling points and condensing temperatures of the gas components. These processes effect separation by cryogenic liquid distillation. Alternatively, if one of the gas components of the gas mixture is a polar or ionizing component, such as carbon dioxide or hydrogen sulfide which readily reacts with aqueous solutions of alkaline chemicals, such as a monoethanolamine or like compounds, separation of the polar or ionizing gas component is commonly effected by solvent absorption.
Both of the above-recited separation mechanisms are capable of a high degree of separation, but require a significant amount of energy input. For example, cryogenic liquid distillation requires significant refrigeration power to liquify the gas mixture, while solvent absorption requires significant process heat for the solvent regeneration and stripping step.
Membrane separation processes, which employ semi-permeable membranes, are typically more energy-efficient than cryogenic liquid distillation or solvent absorption processes. However, the permeation rates for most gas components through currently available polymeric membranes are relatively low. Accordingly, very large membrane surface areas are required to achieve a degree of separation comparable to the above-recited processes. As a result, membrane separation processes typically involve relatively high capital costs. Furthermore, the selectivity of membranes is often relatively poor, resulting in high losses of the more desirable gas component to the reject stream.
The present invention both recognizes and satisfies a need for an alternate relatively energy-efficient, low-cost, highly-effective gas separation process using gas hydrate formation as described hereafter.
An alternate application of the present invention is for the transportation of gas streams such as natural gas from locations which are remote from pipeline markets such as offshore gas fields. One potential solution to the difficulties inherent in transporting a remote natural gas stream is to convert the gas stream to a liquified natural gas (LNG) at or near the gas field where the natural gas is produced in preparation for transport. The natural gas is much more readily transportable in a liquid form. However, the equipment and energy costs for an on-site LNG conversion facility are often impractical. The present invention both recognizes and satisfies a need for an alternate relatively energy-efficient, low-cost, highly-effective gas transportation process using gas hydrate formation as described hereafter.
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