Multiple reflux stream hydrocarbon recovery process
An ethane recovery process utilizing multiple reflux streams is provided. Feed gas is cooled, partially condensed, and separated into a first liquid stream and a first vapor stream. First liquid stream is expanded and sent to a demethanizer. First vapor stream is split into a first and a second separator vapor streams. First separator vapor stream is expanded and sent to demethanizer. Second separator vapor stream is partially condensed and is separated into a reflux separator liquid stream, which is sent to demethanizer, and a reflux separator vapor stream, which is condensed and sent to demethanizer. Demethanizer produces a tower bottom stream containing a substantial amount of ethane and heavier components, and a tower overhead stream containing a substantial amount of remaining lighter components and forms a residue gas stream. A portion of residue gas stream is cooled, condensed, and sent to the demethanizer tower as top reflux stream.
1. A process for separating a gas stream containing methane and ethane, ethylene, propane, propylene and heavier components and heavier hydrocarbons into a volatile gas fraction containing a substantial amount of the methane and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene and heavier components, the process comprising the steps of:
a. splitting a hydrocarbon feed into a first inlet stream, a second inlet stream, and a third inlet stream, and cooling the first and second inlet streams;
b. supplying the first inlet stream and the second inlet stream to a cold separator;
c. separating the first inlet stream and the second inlet stream into a first vapor stream and a first liquid stream;
d. expanding the first vapor stream to produce an expanded first vapor stream and then supplying a demethanizer with the first liquid stream as a first tower feed stream and the expanded first vapor stream as a second tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount methane and lighter components and a demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene and heavier components;
e. warming and compressing the demethanizer overhead stream to produce a residue gas stream; and
f. wherein an improvement comprises the following:
removing at least a portion of the residue gas stream as a residue gas reflux stream;
combining the third inlet stream with the residue gas reflux stream to produce a combined reflux stream and then cooling and partially condensing the combined reflux gas stream to form a partially condensed combined reflux gas stream;
supplying the partially condensed combined reflux gas stream to a reflux separator producing a reflux separator overhead stream and a reflux separator bottoms stream;
supplying the demethanizer with the reflux separator bottoms stream as a third tower feed stream; and
cooling, and substantially condensing and then supplying the demethanizer with the reflux separator overhead stream as a fourth tower feed stream.
2. The process of claim 1 , wherein the step of supplying the first inlet stream and the second inlet stream to a cold separator includes supplying a top of a cold absorber with the first inlet stream and a bottom of the cold absorber with the second inlet stream where the first inlet stream has a temperature colder than the second inlet stream, the cold absorber having a packed bed contained therein.
3. The process of claim 1 , further including subcooling and supplying at least a portion of the first liquid stream to the demethanizer at a feed location located above that of an expanded first separator overhead stream.
4. The process of claim 1 , wherein the steps of supplying the demethanizer with the first, second, third and fourth tower feed streams includes sending the first tower feed stream at a lowest feed location, sending the second tower feed stream at a second tower feed location that is higher than the lowest feed location, sending the third tower feed stream at a third tower feed location that is higher than the second tower feed location, and sending the fourth tower feed stream at a fourth tower feed location that is higher than the third tower feed location.