Recovering gaseous hydrocarbons from tank headspace

1. A method of recovering gaseous hydrocarbons from tank headspace, the method comprising:

flowing a hydrocarbon gas composition from headspace of a tank fed by a primary separator into a compressor to form a compressed mixture, wherein the primary separator accepts a crude hydrocarbon input stream and outputs a crude liquid hydrocarbon stream to the tank, wherein the compressor comprises an oilless compressor, and wherein the oilless compressor comprises a crankcase that is free of oil that contacts material being compressed and is free of oil lubrication that requires regular changings;

flowing the compressed mixture into a cooling unit to cool the compressed mixture, to form a cooled composition comprising liquid hydrocarbons; and

recovering the liquid hydrocarbons as a recovered liquid hydrocarbon stream.

2. The method of claim 1 , wherein the primary separator comprises a two-phase separator.

3. The method of claim 1 , wherein the primary separator outputs a hydrocarbon gas stream to a secondary compressor that generates a compressed gas stream.

4. The method of claim 3 , wherein the secondary compressor comprises an oilless compressor, wherein the oilless compressor comprises a crankcase that is free of oil that contacts material being compressed and is free of oil lubrication that requires regular changings.

5. The method of claim 3 , comprising feeding the compressed gas stream to a secondary separator that outputs a liquid hydrocarbon stream.

6. The method of claim 5 , wherein the secondary separator comprises a heater-treater.

7. The method of claim 5 , comprising feeding the liquid hydrocarbon stream to the primary separator.

8. The method of claim 5 , comprising combining the liquid hydrocarbon stream with the crude hydrocarbon input stream.

9. The method of claim 1 , wherein the flowline from the cooling unit flows the recovered liquid hydrocarbon stream into the primary separator.

10. The method of claim 1 , wherein the flowline from the cooling unit flows the recovered liquid hydrocarbon stream into a hydrocarbon liquid composition output from the primary separator.

11. The method of claim 1 , wherein the flowline from the cooling unit flows the recovered liquid hydrocarbon stream into another separator.

12. The method of claim 1 , further comprising a primary recovery separator that accepts the hydrocarbon gas composition from headspace of the tank fed by the separator and that flows the hydrocarbon gas composition from the primary recovery separator to the compressor.

13. The method of claim 12 , wherein the primary recovery separator comprises a scrubber.

14. The method of claim 1 , further comprising a secondary recovery separator that accepts the cooled composition comprising the liquid hydrocarbons and that outputs the recovered liquid hydrocarbon stream.

15. The method of claim 14 , wherein the secondary recovery separator comprises a separator column.

16. The method of claim 1 , wherein the crude hydrocarbon input stream is from an oil well at an on-shore oil recovery or production facility.

17. The method of claim 1 , wherein the cooling unit comprises an air-cooled heat exchanger.

18. A method of recovering gaseous hydrocarbons from tank headspace, the method comprising:

flowing a hydrocarbon gas composition from headspace of a tank fed by a primary separator into a compressor to form a compressed mixture, wherein the primary separator accepts a crude hydrocarbon input stream, outputs a crude liquid hydrocarbon stream to the tank, and outputs a hydrocarbon gas stream to a secondary compressor that generates a compressed gas stream;

flowing the compressed gas stream to a secondary separator that outputs a liquid hydrocarbon stream;

flowing the liquid hydrocarbon stream to the primary separator;

flowing the compressed mixture into a cooling unit to cool the compressed mixture, to form a cooled composition comprising liquid hydrocarbons; and

recovering the liquid hydrocarbons as a recovered liquid hydrocarbon stream.