Method and system for processing natural gas
Methods and systems for processing natural gas to meet gas pipeline specifications and/or recovering natural gas liquids (NGL). The natural gas is cooled and distilled such that propane and heavier components are produced as a bottoms NGL product, and inerts, methane, ethane, and other lighter portions are produced as a fuel gas grade/quality residue gas product stream. The gas can optionally be treated to remove hydrogen-sulfide and/or carbon dioxide. The NGL product can be split into a marketable propane and butane liquefied petroleum gas (LPG) liquid product and a natural gas condensate product.
1. A system for processing natural gas, the system comprising:
a first compressor for compressing the natural gas into a compressed gas;
a cooling unit for cooling the compressed gas;
a three-way valve downstream of the cooling unit;
an ethylene glycol regeneration unit for injecting ethylene glycol into the cooling unit;
a low-temperature gas-liquid phase separator for: separating the cooled compressed gas into a separator gas, a hydrocarbon liquid and a liquid water/ethylene glycol; directing the separator gas to the cooling unit before filtering and discharge to a natural gas product line as a natural gas product or after compression in a second compressor to a compressed natural gas line as a compressed natural gas product; directing the hydrocarbon liquid to at least one condenser for heating to form a heated hydrocarbon liquid; and directing the liquid water/ethylene glycol to the ethylene glycol regeneration unit;
a deethanizer comprising a top section and a bottom section; the top section configured to separate the heated hydrocarbon liquid into a top section gas and a top section liquid, the top section liquid sent to the bottom section; and the bottom section configured to separate the top section liquid into a bottom section gas and a bottom section liquid, the bottom section gas sent to the top section and the bottom section liquid sent to a natural gas liquids cooler, resulting in a natural gas liquids product for discharge to a natural gas liquids line;
the top section gas sent to the at least one condenser for cooling and condensing into a condenser liquid, the condenser liquid sent to an accumulator with an operating pressure maintained by an accumulator gas control valve, the accumulator separating the condenser liquid into an accumulator gas and an accumulator liquid; and
the accumulator liquid sent to the top section, and the accumulator gas sent to the at least one condenser before being sent to the cooling unit before passing through the three-way valve to selectively direct the accumulator gas to either the natural gas product line for mixing with the natural gas product or to the compressor.
2. The system of claim 1 wherein the cooling unit comprises:
at least one gas/gas exchanger for receiving the compressed gas for pre-cooling to form a pre-cooled compressed gas; and
at least one gas chiller for receiving the pre-cooled compressed gas and cooling the pre-cooled compressed gas to form the cooled compressed gas.
3. The system of claim 1 further comprising a two-phase separator upstream of the first compressor for receiving an initial gas feed stream comprising water and gas, for separating the water from the initial gas feed stream.
4. The system of claim 1 further comprising a first compressor bypass for use in the event that the natural gas is of sufficient pressure to not require compression.
5. The system of claim 1 further comprising a low-pressure separator control valve downstream of the low-temperature gas-liquid phase separator selectively open or as a back pressure control.
6. A method for processing natural gas, the method comprising the steps of:
a. compressing the natural gas into a compressed gas;
b. cooling the compressed gas to form a cooled compressed gas;
c. injecting ethylene glycol into the cooled compressed gas;
d. separating the cooled compressed gas into a separator gas, a hydrocarbon liquid and a liquid water/ethylene glycol;
e. cooling and filtering the separator gas;
f. condensing and heating the hydrocarbon liquid;
g. regenerating ethylene glycol from the liquid water/ethylene glycol;
h. separating the heated hydrocarbon liquid into a first separated gas and a first separated liquid;
i. condensing and cooling the first separated gas;
j. heating the first separated liquid to separate it into a second separated gas and a second separated liquid;
k. cooling the second separated liquid to form a natural gas liquids product; and
l. separating the condensed and cooled first separated gas into a third separated gas and a third separated liquid; condensing and cooling the third separated gas before selectively blending the third separated gas with the natural gas product or compressing the third separator gas.