Process for recovering hydrocarbons from air-hydrocarbon vapor mixtures

An improved process for recovering hydrocarbons from an inlet air-hydrocarbon mixture comprising the steps of:

• (a) flowing said inlet mixture through a first bed of activated carbon whereby said hydrocarbons in said mixture are absorbed on said bed and a residue gas stream comprised of substantially hydrocarbon-free air is produced;
• (b) venting said substantially hydrocarbon-free air to the atmosphere;
• (c) evacuating a second bed of activated carbon having hydrocarbons absorbed thereon by subjecting said bed to pumping with a liquid seal vacuum pump whereby a major portion of said hydrocarbons are desorbed from said bed and a hydrocarbon-rich air-hydrocarbon vapor mixture containing liquid from said liquid sealed vacuum pump and condensed hydrocarbon liquids is produced;
• (e) further evacuating said second bed by vacuum pumping with a positive displacement booster pump connected upstream and in series with said liquid seal vacuum pump while continuing to pump with said liquid seal vacuum pump whereby additional hydrocarbons are desorbed from said bed and additional air-hydrocarbon vapor mixture is produced;
• (e) introducing hydrocarbon-free air into said second bed while continuing to evacuate said bed by vacuum pumping with said booster pump and said liquid seal vacuum pump whereby additional hydrocarbons are stripped from said bed and additional air-hydrocarbon vapor mixture is produced;
• (f) separating the liquid from the liquid seal vacuum pump and the condenses hydrocarbon liquids from each other and from the air-hydrocarbon vapor mixture produced in steps (c), (d) and (e);
• (g) cooling the separated liquid seal vacuum pump liquid;
• (h) recycling the cooled liquid seal vacuum pump liquid to said liquid seal vacuum pump;
• (i) contacting the air-hydrocarbon mixture separated in step (f) in an absorber with a lean liquid absorbent having an affinity for hydrocarbons whereby a major portion of the hydrocarbons are removed therefrom, a hydrocarbon-rich liquid absorbent is produced and a residue gas stream comprised of air and a minor portion of hydrocarbons is produced;
• (j) combining the hydrocarbon liquids separated in step (f) with the hydrocarbon-rich liquid absorbent;
• (k) combining said residue gas stream produced in step (i) with said inlet air-hydrocarbon mixture of step (a) whereby hydrocarbons contained therein are absorbed on said first bed of solid absorbent;
• and
• (l) periodically changing the flow pattern of said inlet air-hydrocarbon mixture and changing the bed of activated carbon being evacuated and stripped whereby when the bed through which the inlet air-hydrocarbon mixture is flowing becomes loaded with absorbed hydrocarbons, the inlet air-hydrocarbon mixture is caused to flow through the bed which has just been evacuated and stripped,
• said positive displacement booster pump being a continuously operating rotary blower having a suction and a discharge and hydrocarbon vapor, air, or a mixture thereof being spilled back from the discharge of said blower to the suction of said blower during step (c) by way of a spillback conduit connected around said blower.

An improved process for recovering hydrocarbons from an inlet air-hydrocarbon vapor mixture comprising the steps of:

• (a) flowing said inlet mixture through a first bed of solid absorbent having an affinity for hydrocarbons whereby hydrocarbons are absorbed on said bed and a residue gas stream comprised of substantially hydrocarbon-free air is produced;
• (b) venting said substantially hydrocarbon-free air to the atmosphere;
• (c) evacuating a second bed of solid absorbent having hydrocarbons absorbed thereon by vacuum pumping with a liquid seal vacuum pump whereby a major portion of said hydrocarbons are desorbed from said bed and a hydrocarbon-rich air-hydrocarbon vapor mixture is produced;
• (d) further evacuating said second bed by vacuum pumping with a positive displacement booster pump connected upstream and in series with said liquid seal vacuum pump while continuing to pump with said liquid seal vacuum pump whereby additional hydrocarbons are desorbed from said bed;
• (e) introducing a quantity of hydrocarbon-free air into said second bed while evacuating said second bed whereby additional hydrocarbons are stripped from said second bed and additional air-hydrocarbon mixture is produced;
• (f) removing a major portion of the hydrocarbons contained in the air-hydrocarbon vapor mixture produced in steps (c), (d), and (e) therefrom whereby a residue gas stream comprised of air and a minor portion of hydrocarbons is produced;
• (g) combining said residue gas stream produced in step (f) with said inlet air-hydrocarbon mixture of step (a) whereby hydrocarbons contained therein are absorbed on said first bed of solid absorbent;
• and
• (h) periodically changing the flow pattern of said inlet air-hydrocarbon mixture and changing the bed of solid absorbent being evacuated whereby when the bed through which the inlet air-hydrocarbon mixture is flowing becomes loaded with absorbed hydrocarbons, the inlet air-hydrocarbon mixture is caused to flow through the bed which has just been evacuated and stripped,
• wherein:
• said first and second beds are each comprised of serially connectable upstream and downstream beds;
• said upstream and downstream beds of said second bed are simultaneously and serially evacuated in step (c) by subjecting said upstream and downstream beds to pumping with said liquid seal vacuum pump;
• only said upstream bed of said second bed is further evacuated in step (d) by vacuum pumping with both said liquid seal vacuum pump and said positive displacement booster pump connected upstream of and in series with said liquid seal vacuum pump, said downstream bed of said second bed being further evacuated simultaneous to the performance of step (d) by vacuum pumping with only said liquid seal vacuum pump;
• a first portion of said hydrocarbon-free air is introduced into said downstream bed in step (e) while continuing to evacuate said downstream bed by vacuum pumping with only said liquid seal vacuum pump;
• and
• a second portion of said hydrocarbon-free air is introduced into said upstream bed in step (e) while continuing to evacuate said upstream bed by vacuum pumping with both said positive displacement booster pump and said liquid seal vacuum pump.