Hydrocarbon vapor recovery processes and apparatus

An improved process and apparatus are provided for recovering hydrocarbons from an intermittent or continuous inlet air-hydrocarbon vapor mixture. The air-hydrocarbon vapor mixture is caused to flow through a bed of solid adsorbent whereby hydrocarbons are removed therefrom and a residue gas stream of substantially hydrocarbon-free air is produced. The substantially hydrocarbon-free air is vented into the atmosphere and a second bed of solid adsorbent having hydrocarbons previously adsorbed thereon is regenerated by evacuation. As long as the concentration of hydrocarbons contained in the vented air is below a predetermined concentration, the inlet air-hydrocarbon vapor mixture is caused to continue to flow through the first bed of adsorbent. After the second bed of adsorbent is regenerated, the pumping and evacuation of the second bed is shut down and not restarted so long as the monitored concentration of hydrocarbons is below the predetermined concentration.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to improved processes and apparatus for 
recovering hydrocarbons from air-hydrocarbon vapor mixtures. 
2. Description of the Prior Art 
In handling multi-component and single component hydrocarbon liquids such 
as gasoline, distillates, benzene and the like, air-hydrocarbon vapor 
mixtures are produced which cannot be vented directly to the atmosphere 
due to the resulting pollution of the environment and fire and/or 
explosion hazard. As a result, various processes and apparatus have been 
developed and used for removing hydrocarbon vapors from air-hydrocarbon 
vapor mixtures whereby the remaining substantially hydrocarbon-free air 
can be safely vented to the atmosphere. The removed hydrocarbons are 
normally liquified and recombined with the hydrocarbon liquid from which 
they were vaporized thereby making their recovery economically 
advantageous. 
A particularly suitable process and apparatus for recovering hydrocarbons 
from air-hydrocarbon vapor mixtures are described in U.S. Pat. No. 
4,276,058 issued to Dinsmore on Jun. 30, 1981. The process, referred to 
herein as the "standard process", basically comprises flowing an inlet 
air-hydrocarbon vapor mixture through a first bed of solid adsorbent 
whereby hydrocarbons are adsorbed on the bed and a residue gas stream 
comprised of substantially hydrocarbon free air which is vented to the 
atmosphere is produced. A second bed of solid adsorbent having 
hydrocarbons adsorbed therein is regenerated by vacuum pumping whereby a 
major portion of the hydrocarbons are desorbed from the bed and a 
hydrocarbon rich air-hydrocarbon mixture is produced. Hydrocarbon-free air 
is injected into the bed being regenerated when high vacuum conditions are 
reached to strip additional hydrocarbons from the bed. A substantial 
portion of the hydrocarbons are recovered from the hydrocarbon rich 
air-hydrocarbon mixture produced during the regeneration. 
The flow pattern of the inlet air-hydrocarbon vapor mixture is periodically 
changed whereby when the bed through which the inlet air-hydrocarbon vapor 
mixture is flowing becomes loaded with adsorbed hydrocarbons, the mixture 
is caused to flow through the bed which has just been evacuated and 
stripped. Before the inlet vapor mixture is switched into the just 
regenerated bed which contains a vacuum, the bed is pressure equalized by 
allowing atmospheric air to enter the bed. Substantially simultaneously 
with the switching of the inlet air-hydrocarbon vapor mixture flow 
pattern, the bed which has just become loaded with adsorbed hydrocarbons 
is changed to regeneration, i.e., to being evacuated and stripped. 
Another particularly suitable process and apparatus for recovering 
hydrocarbons from air-hydrocarbon vapor mixtures are described in U.S. 
Pat. No. 5,154,735 issued to Dinsmore, et al. on Oct. 13, 1992. The 
process, referred to herein as the "high efficiency process", is similar 
to the above described standard process in that it comprises the steps of 
flowing the inlet air-hydrocarbon vapor mixture through a first bed of 
solid adsorbent whereby hydrocarbons are adsorbed on the bed and a residue 
gas stream comprised of substantially hydrocarbon-free air which is vented 
to the atmosphere is produced. A second bed of solid adsorbent having 
hydrocarbons adsorbed thereon is regenerated by vacuum pumping with a 
liquid seal vacuum pump whereby hydrocarbons are desorbed from the bed and 
a hydrocarbon rich air-hydrocarbon mixture is produced. A substantial 
portion of the hydrocarbons are recovered from the hydrocarbon rich 
air-hydrocarbon vapor mixture produced during the regeneration. The beds 
of adsorbent are periodically changed from adsorption to regeneration and 
vice versa as described above in connection with the standard process. 
In accordance with the high efficiency process, the second bed is further 
evacuated by vacuum pumping with a positive displacement booster pump 
connected upstream and in series with the liquid seal vacuum pump while 
continuing to pump with the liquid seal vacuum pump. A relatively high 
rate of hydrocarbon-free air is also injected into the bed being 
regenerated when high vacuum conditions are reached to strip additional 
hydrocarbons from the bed. The further evacuation and higher rate of 
stripping air result in the bed being regenerated to a greater degree and 
a very low hydrocarbon content in the substantially hydrocarbon-free air 
vented to the atmosphere. 
Heretofore, the adsorption, equalization and regeneration cycle times of 
hydrocarbon vapor recovery processes of the types described above have 
typically been short, e.g., about 17 minutes for adsorption, two minutes 
for equalization and 15 minutes for regeneration. In applications of the 
hydrocarbon vapor recovery processes where the flow of the inlet 
air-hydrocarbon vapor mixture is intermittent, e.g., processes for 
recovering vaporized gasoline light ends and the like from a mixture 
thereof with air expelled from tank trucks, the cycle times utilized have 
generally been the same as described above. While different techniques 
have been utilized to conserve power during periods when no inlet 
air-hydrocarbon vapor mixture is available to be processed, such 
techniques heretofore have generally involved shutting the vapor recovery 
apparatus down at the end of a cycle and restarting it when additional 
inlet air-hydrocarbon mixture must be processed. However, because the same 
cycle times are utilized, when the apparatus is operated the vacuum pump 
or pumps and other powered equipment constantly run and power is 
constantly being consumed. Thus, there is a need for improved processes 
and apparatus for recovering hydrocarbons from air-hydrocarbon vapor 
mixtures which can be operated for long periods of time during which the 
inlet flow of the air-hydrocarbon vapor mixture is intermittent without 
operating the regeneration equipment and consuming power. 
Hydrocarbon vapor recovery apparatus of the type described herein have 
heretofore utilized timers or vacuum transmitters to facilitate the 
control of certain aspects of the process. For example, U.S. Pat. No. 
5,591,254 issued to Gibson on Jan. 7, 1997 discloses a vapor recovery 
apparatus with an automatic flow control system which includes a vacuum 
transmitter for monitoring pressure within the apparatus at selected 
points and controlling the operation of the valves in response thereto. 
While a vacuum transmitter can be utilized in conjunction with a valve 
controller as described in the Gibson patent, the vacuum transmitter 
readings are affected by site elevation and variations in atmospheric 
pressure which causes a certain amount of inherent inaccuracy in the 
operation of the system. Thus, there is a need for an improved vapor 
recovery process and apparatus which are controlled in certain aspects by 
accurate measurements of the pressure levels within the adsorbent beds 
being regenerated and related equipment. 
Finally, in the heretofore utilized vapor recovery apparatus, a three-phase 
separator has been utilized in conjunction with the liquid seal vacuum 
pump. The three-phase separator has generally been a vessel divided into 
two sections by an internal baffle which allows vapor and condensed 
hydrocarbons to flow over the top of the baffle into the absorber side of 
the vessel to which an absorber is attached. Such a three-phase separator 
is described in the above mentioned U.S. Pat. No. 5,154,735. In order to 
eliminate carry-over of the vacuum pump seal liquid into the absorber side 
of the vessel, a full diameter wire mesh mist extractor has been employed 
on the vacuum pump seal fluid side of the vessel to coalesce the seal 
fluid and eliminate carry-over. When the mist extractor must be serviced 
and cleaned, it is necessary to enter the vessel which is time consuming 
and requires a relatively long shut-down time. Thus, there is a need for 
an improved three-phase separator for use in hydrocarbon vapor recovery 
apparatus of the type described herein. 
SUMMARY OF THE INVENTION 
The present invention provides improved processes and apparatus for 
recovering hydrocarbons from intermittent or continuous inlet air 
hydrocarbon vapor mixtures which meet the needs described above and 
overcome the deficiencies of the prior art. 
The improved processes of the present invention are basically comprised of 
the following steps. An inlet air-hydrocarbon vapor mixture is flowed 
through a first bed of adsorbent whereby hydrocarbons in the mixture are 
adsorbed on the bed and a residue gas stream comprised of substantially 
hydrocarbon-free air is produced. The substantially hydrocarbon-free air 
is vented to the atmosphere and the concentration of hydrocarbons 
contained in the vented substantially hydrocarbon-free air is continuously 
monitored. The flow of the inlet air-hydrocarbon mixture through the first 
bed is continued, either intermittently or continuously, so long as the 
monitored concentration of hydrocarbons in the vented substantially 
hydrocarbon-free air is below a predetermined concentration. A second bed 
of adsorbent having hydrocarbons adsorbed thereon is regenerated by 
subjecting the bed to pumping with a vacuum pump and air stripping whereby 
hydrocarbons are desorbed from the bed and a hydrocarbon rich 
air-hydrocarbon vapor mixture is produced. A major portion of the 
hydrocarbons are recovered from the hydrocarbon rich air-hydrocarbon vapor 
mixture and the remaining air-hydrocarbon vapor mixture is combined with 
the inlet air-hydrocarbon mixture flowing to the first bed of adsorbent. 
The vacuum pumping and evacuation of the second bed is terminated after a 
major portion of the hydrocarbons are desorbed therefrom, and the 
termination is continued for so long as the monitored concentration of 
hydrocarbons in the substantially hydrocarbon-free air which is vented to 
the atmosphere is below the predetermined concentration. The process is 
continued by flowing the inlet air-hydrocarbon mixture through the first 
bed of adsorbent without further regeneration of the second bed until the 
monitored concentration of hydrocarbons contained in the vented 
substantially hydrocarbon-free air equals or exceeds the predetermined 
concentration, at which time the flow pattern of the inlet air-hydrocarbon 
mixture is changed whereby it is flowed through the regenerated bed of 
adsorbent and the bed of adsorbent previously adsorbing hydrocarbons from 
the inlet vapor mixture is regenerated. 
The processes preferably also include the step of monitoring the absolute 
pressure in the bed of adsorbent being regenerated and the absolute 
suction pressure of the liquid seal vacuum pump during regeneration. The 
monitored absolute pressures are utilized in conjunction with an 
electronic valve and pump controller to introduce stripping gas into the 
adsorbent bed being evacuated at a preselected absolute pressure level, 
and for restricting the rate at which hydrocarbons are desorbed from the 
second bed for an initial time period during the evacuation of the second 
bed until a preselected absolute pressure is reached in the second bed. 
Further, when a positive displacement booster pump is utilized in 
combination with the liquid seal vacuum pump in a high efficiency process, 
the vacuum pumping by the booster pump is started at a preselected 
absolute pressure in the adsorbent bed being regenerated and the rate of 
pumping is restricted for an initial time period after the pumping starts 
until a preselected absolute suction pressure is reached by the liquid 
seal vacuum pump. 
An improved hydrocarbon rich liquid absorbent accumulator or condensed 
hydrocarbon accumulator and a three-phase separator for separating vacuum 
pump seal liquid, condensed hydrocarbons and an air-hydrocarbon vapor 
mixture from each other are also provided. The accumulator and three-phase 
separator are separate compartments of a single vessel sealingly divided 
by a wall therein. A mist extractor is removably disposed across a top 
outlet connection of the three-phase separator compartment and a dip tube 
is disposed in the liquid absorbent accumulator compartment sealingly 
connected to an opening in the wall for conducting condensed hydrocarbons 
from the three-phase separator compartment to the liquid absorbent 
accumulator compartment thereof. 
It is, therefore, a general object of the present invention to provide an 
improved hydrocarbon vapor recovery process and apparatus. 
Other and further objects, features and advantages of the present invention 
will be readily apparent to those skilled in the art upon a reading of the 
description of preferred embodiments which follows when taken into 
conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 1, apparatus for carrying out an improved standard 
process of the present invention is illustrated and generally designated 
by the numeral 10. The apparatus 10 is comprised of a pair of adsorbers 12 
and 14, each of which contains a bed of solid adsorbent through which 
gases can flow. Each of the adsorbers 12 and 14 are closed vessels and 
include connections on opposite sides of the beds of adsorbent therein. 
That is, the adsorber 12 includes inlet and outlet connections 16 and 18 
and the adsorber 14 includes inlet and outlet connections 20 and 22. While 
various solid adsorbents having an affinity for hydrocarbons can be 
utilized in the adsorbers 12 and 14, activated carbon is preferred. 
An air-hydrocarbon vapor mixture inlet header 24 is provided connected to a 
conduit 26 which conducts a mixture of air and hydrocarbon vapor, e.g., 
gasoline vapor or the like, from a source thereof to the apparatus 10. A 
pair of conduits 28 and 30 are connected to the header 24 and to the inlet 
connections 16 and 20 of the adsorbers 12 and 14, respectively. 
Conventional switching valves 32 and 34 are disposed in the conduits 28 
and 30, respectively, and a header 36 is connected to the conduits 28 and 
30 at points thereon between the switching valves 32 and 34 and the 
connections 16 and 20 of the adsorbers 12 and 14. A pair of switching 
valves 38 and 40 are disposed in the header 36 and a conduit 42 is 
connected to the header 36 at a point between the switching valves 38 and 
40. 
A residue gas header 44 is provided and a pair of conduits 46 and 48 are 
connected to the header 44 and to the connections 18 and 22 of the 
adsorbers 12 and 14. Switching valves 50 and 52 are disposed in the 
conduits 46 and 48, respectively, and a conduit 54 is connected to the 
header 44 for venting substantially hydrocarbon-free air to the 
atmosphere. A conduit 56 connected to a source of stripping air or other 
inert gas, which can optionally be heated, is connected to a stripping air 
inlet connection 58 in the adsorber 12. A switching valve 60 is disposed 
in the conduit 56. In a like manner, stripping air is conducted to the 
adsorber 14 by conduit 62 connected to a connection 64 in the adsorber 14. 
A switching valve 66 is disposed in the conduit 62. 
The other end of the conduit 42 connected to the header 36 is connected to 
the suction connection 68 of a conventional liquid seal vacuum pump 70. 
The liquid seal vacuum pump 70 also includes a seal liquid inlet 
connection 72 and a discharge connection 74 from which seal liquid, 
condensed hydrocarbons and an air-hydrocarbon vapor mixture are discharged 
as will be further described hereinbelow. A conduit 76 is connected to the 
discharge connection 74 of the liquid seal vacuum pump 70 and to an inlet 
connection 77 of a combined three-phase separator and hydrocarbon rich 
liquid absorbent accumulator vessel 78. 
The vessel 78 is divided internally into two separate sealed compartments 
80 and 82 by a wall 84. The three-phase separator compartment 80 includes 
the inlet connection 77 for receiving seal liquid, condensed hydrocarbons 
and an air-hydrocarbon vapor mixture from the liquid seal vacuum pump 70. 
The liquid absorbent accumulator compartment 82 and the three-phase 
separator compartment 80 each include a vapor mixture connection in the 
top thereof. That is, the liquid absorbent accumulator compartment 82 
includes a top connection 86 and the three-phase separator compartment 80 
includes a top connection 88. A conduit 90 is sealingly connected to and 
between the top connections 86 and 88 for conducting a separated 
air-hydrocarbon vapor mixture from the three-phase separator compartment 
80 to the liquid absorbent accumulator compartment 82. A mist extractor 92 
is removably disposed across the top outlet connection 88 of the 
three-phase separator compartment 80 so that when the conduit 90 is 
removed from the vessel 78, the mist extractor 92 can quickly be inspected 
and removed and cleaned if necessary. An outlet connection 94 is provided 
in the bottom of the three-phase separator compartment 80 for removing 
vacuum pump seal liquid therefrom. An opening 96 is disposed in the wall 
which sealingly divides the compartments 80 and 82, and a dip tube 98 is 
disposed in the liquid absorbent accumulator compartment 82 which is 
sealingly connected to the opening 96 in the wall 84. The dip tube 98 
conducts condensed hydrocarbons from the three-phase separator compartment 
80 to the bottom of the liquid absorbent accumulator compartment 82. An 
outlet connection 100 is disposed in the bottom of the liquid absorbent 
accumulator compartment 82 for removing rich liquid absorbent and 
condensed hydrocarbons therefrom. An absorber 102 is integrally connected 
to the top of the vessel 78, but as will be understood by those skilled in 
the art, the absorber 102 and the vessel 78 can be separate vessels if 
necessary or desired. 
The three-phase separator compartment 80 of the vessel 78 functions to 
separate the seal liquid utilized for the pump 70, the hydrocarbon rich 
air-hydrocarbon vapor mixture removed from the bed of adsorbent being 
regenerated and hydrocarbons which condense therefrom. The seal liquid is 
typically water containing a freezing point depressant such as ethylene 
glycol. As indicated above, the separated seal liquid is withdrawn from 
the compartment 80 by way of the connection 94 thereof and the separated 
air-hydrocarbon vapor mixture is withdrawn from the compartment 80 by way 
of the connection 88 at the top of the compartment 80, the mist extractor 
92, and the conduit 90. The condensed hydrocarbons which are lighter than 
the seal liquid and accumulate on top of the seal liquid in the 
compartment 80 is removed therefrom by way of the opening 96 in the wall 
84 and the dip tube 98. The dip tube 98 conducts the condensed 
hydrocarbons to below the surface of a body 104 of condensed hydrocarbons 
and rich liquid absorbent accumulated in the bottom of the liquid 
adsorbent accumulator compartment 82. The separated hydrocarbon rich 
air-hydrocarbon vapor mixture which flows into the compartment 82 from the 
three-phase separator compartment 80 flows into the bottom of the absorber 
102 as will be described further. 
The seal liquid separated in the three-phase separator compartment 80 is 
withdrawn therefrom by a conduit 106 connected between the connection 94 
and the seal liquid inlet connection 72 of the liquid seal vacuum pump 70. 
A cooler 108 is disposed in the conduit 106 for cooling the seal liquid as 
it flows therethrough. While the cooler 108 can be of various types and 
designs, a heat exchanger which cools the seal liquid by passing it in 
heat exchange relationship with a stream of lean liquid used as the 
absorption medium in the absorber 102 is preferred and generally is the 
most economical. 
A conduit 110 is connected to the outlet connection 100 of the rich liquid 
absorbent accumulator compartment 82 and to a pump 112. The discharge of 
the pump 112 is connected to a conduit 164 which leads the rich liquid 
absorbent and condensed hydrocarbon liquid mixture withdrawn from the 
compartment 82 to a storage facility (not shown). 
The absorber 102 is connected to an opening 103 in the top of the liquid 
absorbent accumulator 82. The absorber 102 includes means disposed therein 
for bringing about intimate contact between a liquid adsorbent flowing 
downwardly therein and a vapor mixture flowing upwardly therein. Such 
means can be comprised of vapor-liquid contact trays or any of a variety 
of conventional packing material. Preferably, the absorber 102 includes a 
section of packing material 114 disposed in the top portion thereof for 
bringing about the intimate contact. A residue gas outlet connection 116 
and a lean liquid absorbent inlet connection 118 are provided above the 
packed section 114. The hydrocarbon rich liquid absorbent from the 
absorber 102 enters the compartment 82 by way of the opening 103 therein. 
The hydrocarbon rich liquid absorbent accumulates in the compartment 82 
along with condensed hydrocarbon liquid which enters the compartment 82 by 
way of the dip tube 98 from the three-phase separator compartment 80 as 
previously described. 
The separated hydrocarbon rich air-hydrocarbon mixture produced from the 
regeneration of an adsorbent bed flows from the compartment 82 upwardly 
through the open bottom of the absorber 102 into contact with liquid 
absorbent flowing downwardly therein whereby hydrocarbons are absorbed and 
removed from the vapor mixture and a residue gas stream comprised of air 
and a minor portion of hydrocarbons is produced. 
A conduit 120 is connected to the lean liquid absorbent inlet connection 
118 of the absorber 102 and to the discharge connection of a pump 122. A 
conduit 124 is connected to the suction connection of the pump 122 which 
leads a stream of lean liquid absorbent from a source thereof such as a 
storage tank to the pump 122. A conduit 126 connected to the conduit 120 
conducts a slip stream of lean liquid absorbent to the heat exchanger 108 
wherein it exchanges heat with and cools the seal liquid flowing to the 
liquid seal vacuum pump 70. A conduit 128 conducts the lean liquid 
absorbent from the heat exchanger 108 to an inlet connection 130 in the 
absorber 102. 
As mentioned above, when it is necessary to inspect and/or clean the mist 
extractor 92 removably disposed within and across the outlet connection 88 
of the three-phase separator compartment 80, the conduit 90 is 
disconnected from the connections 88 and 86 and removed therefrom. The 
mist extractor 92 is removed from the vessel 78, inspected, cleaned and/or 
replaced, and the conduit 90 is reconnected to the connections 88 and 86. 
Because of the presence of the mist extractor 92 and because the 
three-phase separator and hydrocarbon rich liquid absorbent compartments 
are sealingly separated, carry-over of seal liquid between the 
compartments is prevented. Further, because the dip tube 98 conducts 
condensed liquid hydrocarbons from the three-phase separator compartment 
80 to below the surface of the body of liquid 104 in the compartment 82, 
the air-hydrocarbon vapor mixture separated in the compartment 80 must 
flow through the mist extractor 92 and conduit 90 and is prevented from 
flowing between the compartments 80 and 82 within the vessel 78. 
The residue gas stream produced in the absorber 102 exits the absorber 102 
by way of the connection 116 thereof and flows through a conduit 166 
connected between the connection 116 and the inlet air-hydrocarbon vapor 
header 24. A conduit 132 for recycling an air-hydrocarbon vapor mixture 
through the liquid seal vacuum pump 70 during the pressure equalizing 
cycle is connected between the conduit 166 and the conduit 42. A switching 
valve 134 is disposed in the conduit 132. 
A conventional electronic valve and pump controller 136 is provided for 
operating the switching valves 32, 34, 38, 40, 50, 52, 60, 66 and 134 as 
well as the liquid seal vacuum pump 70 and the liquid absorbent pumps 112 
and 122 in a manner which will be described further hereinbelow. A 
particularly suitable such controller is a Programmable Logic Controller 
commercially available from the General Electric Corp. under the trade 
designation "GE 9030.RTM.". An absolute pressure transmitter 138 is 
connected to the conduit 42 to thereby sense the absolute suction pressure 
of the liquid seal vacuum pump 70 and the absolute pressure in the 
adsorbent bed being regenerated. The output signal from the transmitter is 
connected to the valve and pump controller 136. The use of an absolute 
pressure transmitter instead of a conventional vacuum transmitter 
eliminates errors introduced by changes in elevation and atmospheric 
pressure. A particularly suitable absolute pressure transmitter is 
commercially available from the Rosemount Company under the trade 
designation "Rosemount Model 2088A-1-A-22-A-1-B4-E5-M7.RTM.". Also, a 
hydrocarbon concentration monitor 140 is connected to the substantially 
hydrocarbon-free air vent conduit 54 and the output signal therefrom is 
connected to the valve and pump controller 136. 
OPERATION OF THE APATUS 10 
In operation of the apparatus 10, the switching valves 32, 34, 38, 40, 50 
and 52, are operated by the valve and pump controller 136 in a manner 
whereby the inlet air-hydrocarbon vapor mixture is caused to flow through 
one of the adsorbers 12 or 14 while the other of the adsorbers is being 
regenerated. For example, during a first cycle, the switching valve 34 is 
open and the switching valve 32 is closed whereby the inlet 
air-hydrocarbon vapor mixture flows into the adsorber 14 from the header 
24 by way of the conduit 30, the switching valve 34 therein and the 
connection 20 in the adsorber 14. Because the switching valve 32 disposed 
in the conduit 28 is closed, the inlet air-hydrocarbon vapor mixture is 
prevented from entering the adsorber 12. The switching valve 52 disposed 
in the conduit 48 is also open and the switching valve 50 disposed in the 
conduit 46 is closed whereby the residue gas stream produced in the 
adsorber 14 exits the adsorber 14 by way of the connection 22 thereof, the 
conduit 48 and the switching valve 52 and enters the header 44. From the 
header 44, the residue gas stream flows through the conduit 54 from where 
it is vented to the atmosphere. The switching valve 40 disposed in the 
header 36 is closed and the switching valve 38 disposed therein is open 
whereby the adsorbent bed within the adsorber 12 is communicated with the 
suction connection 68 of the liquid seal vacuum pump 70 by way of the 
connection 16 of the adsorber 12, the header 36, the open switching valve 
38 and the conduit 42. The switching valve 66 disposed in the stripping 
air conduit 62 connected to the stripping air inlet connection 64 of the 
adsorber 14 is closed. The switching valve 60 disposed in the stripping 
air conduit 56 connected to the stripping air inlet connection 58 of the 
adsorber 12 is initially closed and then opened during a later part of the 
regeneration of the bed of adsorbent in the adsorber 12 as will be further 
described herein below. 
During a first part of the cycle when the switching valves are in the mode 
described above, the inlet air-hydrocarbon vapor mixture flows through the 
bed of adsorbent within the adsorber 14 so that hydrocarbons are adsorbed 
on the bed and removed from the mixture. The residue gas produced which is 
comprised of substantially hydrocarbon-free air is vented to the 
atmosphere by way of the air vent pipe 54. Simultaneously, the bed of 
adsorbent disposed within the adsorber 12 is evacuated by the liquid seal 
vacuum pump 70 whereby hydrocarbons are desorbed therefrom. A hydrocarbon 
rich air-hydrocarbon vapor mixture is withdrawn from the adsorbent bed 
within the adsorber 12 which flows through the vacuum pump 70. Cooled seal 
liquid, preferably water containing a freezing point depressant such as 
ethylene glycol, flows into the vacuum pump 70 by way of the inlet 
connection 72 thereof and is discharged by way of the discharge connection 
74 along with the hydrocarbon-rich air-hydrocarbon vapor mixture and 
hydrocarbons condensed therefrom. That is, the intimate contact of the 
hydrocarbon-rich air-hydrocarbon vapor mixture with the cool seal liquid 
while flowing through the vacuum pump 70 cools the vapor mixture and 
causes hydrocarbons contained therein to be condensed. Thus, a stream of 
hydrocarbon-rich air-hydrocarbon vapor mixture containing seal liquid and 
condensed hydrocarbon liquids exits the pump 70 and flows through the 
conduit 76 into the three-phase separator compartment 80 of the vessel 78. 
While passing through the separator compartment 80, the air-hydrocarbon 
vapor mixture, seal liquid and condensed hydrocarbon liquids are separated 
from each other as previously described. The seal liquid which is 
discharged from the three-phase separator compartment 80 by way of the 
connection 94 thereof and the conduit 106 is continuously circulated 
between the three-phase separator compartment 80, the seal liquid cooler 
108 and the vacuum pump 70 while the vacuum pump 70 is operating. As also 
mentioned, the separated condensed hydrocarbons flow into the accumulator 
compartment 82 of the vessel 78 by way of the dip tube 98 where they 
combine with rich liquid absorbent flowing into the compartment 82 from 
the absorber 102. The condensed hydrocarbons and rich liquid absorbent are 
removed from the compartment 82 by way of the connection 100 thereof, the 
conduit 110 and the pump 112. From the pump 112, the rich liquid 
absorbent-condensed hydrocarbon liquid mixture is conducted by way of a 
conduit 164 to storage facilities or a point of further processing (not 
shown). 
A first stream or portion of lean liquid absorbent is pumped from a source 
thereof by the pump 122 to the seal liquid cooler 108 by the conduits 120 
and 126. The first portion of the liquid absorbent which is heated in the 
cooler 108 is conducted therefrom by the conduit 128 and flows into the 
absorber 102 by way of the inlet connection 130 located in a lower portion 
of the absorber 102. The first portion of liquid absorbent is intimately 
contacted with the hydrocarbon-rich air-hydrocarbon vapor mixture flowing 
upwardly in the absorber 102. A second stream or portion of the lean 
liquid absorbent is pumped by the pump 122 and flows by way of the conduit 
120 and the connection 118 in the upper portion of the absorber 102 into 
the absorber 102. The second portion of the lean liquid absorbent flows 
downwardly within the absorber 102 through the packed section 114 thereof 
and intimately contacts the air-hydrocarbon vapor mixture flowing upwardly 
therethrough. As the hydrocarbon rich air-hydrocarbon vapor mixture flows 
upwardly through the absorber 102, it is contacted by the liquid absorbent 
flowing downwardly therein whereby hydrocarbons are absorbed in the liquid 
absorbent and removed from the vapor mixture and the hydrocarbon-rich 
liquid absorbent which flows into the accumulator compartment 82 is 
produced. A residue gas stream comprised of air and a minor portion of 
hydrocarbons is also produced which exits the absorber 102 by way of the 
discharge connection 116 in the top thereof. The residue gas stream is 
conducted by the conduit 166 into the header 24 where it combines with the 
inlet air-hydrocarbon vapor mixture and flows through the adsorber 14. As 
will be understood, the hydrocarbons contained in the residue gas stream 
are adsorbed on the bed of adsorbent within the adsorber 14 along with 
hydrocarbons from the inlet air-hydrocarbon vapor mixture. 
During a later part of the cycle, after a major portion of hydrocarbons 
adsorbed on the bed of adsorbent within the adsorber 14 have been desorbed 
therefrom by the operation of the vacuum pump 70, the stripping air 
switching valve 60 in the conduit 56 is opened whereby a quantity of 
hydrocarbon-free air from the atmosphere enters the conduit 56 and flows 
into the adsorber 12. The hydrocarbon-free air flows through the bed of 
adsorbent within the adsorber 12 which is at high vacuum condition and 
causes additional hydrocarbons to be stripped from the bed which were not 
desorbed therefrom by vacuum pumping alone. 
In accordance with the present invention, the concentration of hydrocarbons 
in the substantially hydrocarbon-free air vented to the atmosphere by way 
of the air vent 54 is continuously monitored by the hydrocarbon 
concentration monitor 140 connected to the vent pipe 54. As mentioned 
above, the output signal from the hydrocarbon monitor 140 is connected to 
the valve and pump controller 136 and so long as the monitored hydrocarbon 
concentration in the vent stream is below a predetermined concentration, 
the flow of inlet air-hydrocarbon vapor mixture through the bed of 
adsorbent in the adsorber 14 is continued. 
After the bed of adsorbent in the adsorber 12 has been regenerated by 
pumping with the liquid seal vacuum pump 70 and stripping with stripping 
air whereby a major portion of the hydrocarbons are desorbed from the bed, 
the regeneration of the bed of adsorbent in the adsorber 12 is terminated. 
That is, the liquid seal vacuum pump 70 and the liquid absorbent pumps 112 
and 122 are shut-down. Thereafter, the flow of the inlet air-hydrocarbon 
vapor mixture through the bed of adsorbent in the adsorber 14 and the 
shut-down of the above mentioned regeneration pumps is continued for so 
long as the monitored concentration of hydrocarbons in the vented 
substantially hydrocarbon-free air is below the predetermined 
concentration. 
When the monitored concentration of hydrocarbons in the vented 
substantially hydrocarbon-free air becomes equal to or above the 
predetermined concentration, the vacuum which exists in the regenerated 
bed of adsorbent within the adsorber 12 is equalized by closing the 
switching valve 38 in the header 36 and starting the liquid seal vacuum 
pump 70 and absorbent pumps 112 and 122. The absolute pressure transmitter 
138 monitors the absolute suction pressure of the liquid seal vacuum pump 
70 and sends an output signal to the valve and pump controller 136. At a 
preselected absolute vacuum pump suction pressure, the controller 136 
opens the valve 134 in the conduit 132 whereby an air-hydrocarbon vapor 
mixture is recycled through the liquid seal vacuum pump during the time 
that the switching valve 38 is closed and the regeneration system is 
isolated from the adsorbers 12 and 14. The controller 136 slowly opens the 
switching valve 50 in the conduit 46 whereby substantially 
hydrocarbon-free air is allowed to back-flow from the header 44 into the 
adsorber 12 by way of the connection 18 thereof. When the pressure within 
the adsorber 12 reaches substantially atmospheric pressure, the switching 
valve 32 in the conduit 28 is opened and the switching valve 34 in the 
conduit 30 is closed whereby the inlet air-hydrocarbon vapor mixture flows 
through the regenerated bed of adsorbent in the adsorber 12. Substantially 
simultaneously therewith, the switching valve 52 in the conduit 48 is 
closed, and thereafter, the switching valve 40 in the header 36 slowly 
opens whereby the bed of adsorbent within the adsorber 14 is regenerated 
by evacuation and stripping as described above. Once the switching valve 
40 has initially opened whereby the bed of adsorbent within the adsorber 
14 has begun to be evacuated, the switching valve 134 in the conduit 132 
is closed whereby the recycle of the air-hydrocarbon vapor mixture between 
the vacuum pump 70 and the vessel 78 and adsorber 102 is terminated until 
the next equalization cycle. After the beds of adsorbent have changed, the 
above described procedure is repeated whereby the bed adsorbing 
hydrocarbons from the inlet air-hydrocarbon vapor mixture is continued so 
long as the monitored hydrocarbon concentration of the vented 
substantially hydrocarbon-free air remains below the predetermined 
concentration and after the other bed of absorbent is regenerated, the 
regeneration system is shut-down to conserve the consumption of power. 
As will now be understood by those skilled in the art, the flow pattern of 
the inlet air-hydrocarbon vapor mixture and the bed being regenerated are 
changed or cycled based on the monitored hydrocarbon concentration in the 
substantially hydrocarbon-free air vented to the atmosphere. That is, 
after equalization as described above, the inlet mixture is cause to flow 
through the bed which has just been regenerated and the bed which has just 
adsorbed hydrocarbons from the inlet mixture is subjected to regeneration. 
The hydrocarbon-rich air-hydrocarbon vapor mixture produced from the bed 
being regenerated is contacted with liquid absorbent in the absorber 102 
whereby a major portion of the hydrocarbons therein are recovered. 
As previously described, the absolute pressure in the bed being regenerated 
is monitored by the absolute vacuum transmitter 138. If the absolute 
regeneration pressure is too high at the end of a regeneration cycle, the 
pump and valve controller 136 displays a warning to that effect whereby 
the operator of the apparatus 10 can take appropriate steps to remedy the 
situation. Also, the controller 136 uses the absolute regeneration 
pressure monitored by the absolute vacuum transmitter 138 to slowly stage 
open the regeneration switching valves 38 and 40 as described above. That 
is, at the beginning of each regeneration cycle, one of the regeneration 
switching valve 38 or 40 is initially slowly opened based on the monitored 
absolute regeneration pressure so that the vacuum pump 70 and other parts 
of the regeneration system are not overloaded. The slow staged opening of 
the regeneration valves restricts the rate at which hydrocarbons are 
desorbed from the bed of adsorbent being regenerated for an initial time 
period during the regeneration cycle. 
As will also now be understood, in accordance with the present invention, 
the inlet air-hydrocarbon vapor mixture which can be intermittent or 
continuous is allowed to flow through the bed of adsorbent which is 
adsorbing hydrocarbons from the mixture for as long as the monitored 
hydrocarbon concentration in the vented substantially hydrocarbon-free air 
is below a preselected concentration. After the bed being regenerated has 
been subjected to regeneration for a normal cycle time, the regeneration 
can optionally be extended for an additional time to insure that the bed 
is fully regenerated. The regeneration equipment is then shut-down and can 
remain shut-down until the predetermined hydrocarbon concentration in the 
vented substantially hydrocarbon-free air is exceeded whereupon the beds 
are changed and the procedure repeated. 
The process of the present invention is preferably controlled (by the 
controller 136) whereby if during any regeneration cycle, the 
predetermined hydrocarbon concentration of the vented substantially 
hydrocarbon-free air is equaled or exceeded, the regeneration of the bed 
of adsorbent in progress will continue to the end of a first normal cycle. 
If the bed being regenerated is in an extended cycle, the beds of 
adsorbent are immediately switched. The process can optionally be 
controlled to switch the beds after a relatively long time period even if 
the hydrocarbon concentration in the vented substantially hydrocarbon-free 
air has not been equaled or exceeded. For example, the valve controller 
136 can be set to switch the beds on a time cycle in the range of from 
about 1 hour to about 24 hours, preferably about 12 hours, even though the 
hydrocarbon concentration of the vented stream has not been equaled or 
exceeded. 
Referring now to FIG. 2, apparatus for carrying out an improved high 
efficiency process of the present invention is illustrated and generally 
designated by the numeral 150. The apparatus 150 is identical to the 
apparatus 10 previously described except for the addition of a second 
absolute pressure transmitter 162 the output signal of which is connected 
to the controller 136, a positive displacement booster pump 152, a conduit 
158 and a spill-back valve 160 utilized with the booster pump 152. 
Accordingly, FIG. 2 includes a number of the same character references as 
are used in FIG. 1 which refer to the same parts as those shown in FIG. 1. 
The positive displacement booster pump 152 includes an inlet connection 154 
and an outlet connection 156, and the booster pump is disposed in the 
conduit 42 upstream and in series with the liquid seal vacuum pump 70. The 
conduit 158 is connected to the conduit 42 on both sides of the booster 
pump 152 and the spill-back control valve 160 is disposed in the conduit 
158. The second absolute pressure transmitter 162 is connected to the 
conduit 42 upstream of the booster pump 152 so that it continuously 
monitors the absolute pressure in the adsorber being regenerated. The 
absolute pressure transmitter 138 continuously monitors the absolute 
suction pressure of the liquid seal vacuum pump 70. 
OPERATION OF THE APATUS 150 
The operation of the apparatus 150 illustrated in FIG. 2 is identical to 
the above described operation of the apparatus 10 with respect to the 
periodic changing of the flow pattern of the inlet air-hydrocarbon vapor 
mixture and the switching of the beds of adsorbent from adsorbing 
hydrocarbons to regeneration. The operations of the liquid seal vacuum 
pump 70, the three-phase separator compartment 80 of the vessel 78, the 
condensed hydrocarbon and rich liquid absorbent accumulator compartment 82 
of the vessel 78, the absorber 102, the liquid absorbent pumps 112 and 
122, the cooler 108 and the recycle valve 134 in the conduit 132 are also 
identical to the operations of such apparatus described in connection with 
the apparatus 10. 
During the regeneration of a bed of adsorbent, e.g., the bed of adsorbent 
in the adsorber 12, the bed of adsorbent is first evacuated by the liquid 
seal vacuum pump 70 whereby hydrocarbons are desorbed therefrom. A 
hydrocarbon rich air-hydrocarbon vapor mixture is withdrawn from the 
adsorbent bed within the adsorber 12 which flows through the vacuum pump 
70 as described above in connection with the apparatus 10. During this 
first part of the regeneration cycle, the booster pump 152 is continuously 
operated, but the spill-back valve 160 disposed in the conduit 158 is open 
whereby the booster pump 152 is unloaded and the vacuum created in the 
absorber 12 is produced by the liquid seal vacuum pump 70 alone. During 
the regeneration cycle, the valve and pump controller 136 slowly stage 
closes the spill-back valve 160. The slow staged closing of the spill-back 
valve 160 restricts the rate of pumping by the booster pump 152 for an 
initial time period after it begins pumping until a preselected absolute 
suction pressure as monitored by the transmitter 138 is reached by the 
liquid seal vacuum pump 70. The slow closing of the spill-back valve 160 
brings about maximum pumping capacity without overloading the liquid seal 
vacuum pump 70 and the downstream components of the regeneration 
apparatus. Once the spill-back valve 160 is fully closed and the booster 
pump 152 is fully loaded, a suction is produced in addition to the suction 
produced by the liquid seal vacuum pump 70 which is exerted on the bed of 
adsorbent within the adsorber 12 thereby creating a deeper vacuum, further 
evacuating the bed of adsorbent within the adsorber 12 and causing 
additional hydrocarbons to be desorbed therefrom. 
During the last part of the regeneration cycle, after a major portion of 
hydrocarbons adsorbed on the bed of adsorbent within the adsorber 12 have 
been desorbed therefrom by the operation of the liquid seal vacuum pump 70 
and the booster pump 152, the switching valve 60 in the stripping air 
conduit 56 is opened whereby a quantity of hydrocarbon free stripping air 
flows into the adsorber 12. As described above in connection with the 
apparatus 10, the stripping air flows through the bed of adsorbent 
contained in the adsorber 12 and is withdrawn therefrom by the booster 
pump 152 and the liquid seal vacuum pump 70. 
As mentioned, the absolute pressure transmitter 138 continuously monitors 
the vacuum pump suction pressure. It also opens the vacuum control valve 
134 during the pressure equalization cycle as described above with respect 
to the apparatus 10. The second absolute pressure transmitter 162 
functions in conjunction with the valve and pump controller 136 to open 
the stripping air control valves 60 or 66 when a predetermined absolute 
regeneration pressure is reached in the adsorbent bed being regenerated. 
It also functions in conjunction with the controller 136 to stage open the 
regeneration valves 38 or 40 whereby the rate at which hydrocarbons are 
desorbed from the bed of adsorbent being regenerated is restricted for an 
initial time period until a preselected absolute pressure is reached. 
Finally, the second absolute pressure transmitter 162 monitors the 
regeneration pressure and the controller 136 displays a warning if it is 
too high after a predetermined time. 
The overall operation of the apparatus 150 and the process carried out 
thereby is the same as the operation described above in connection with 
the apparatus 10. Thus, the flow pattern of the inlet air-hydrocarbon 
vapor mixture and the bed being regenerated are changed, i.e., cycled, 
based on the continuously monitored hydrocarbon concentration in the 
substantially hydrocarbon-free air vented to the atmosphere. Also, the 
inlet air-hydrocarbon vapor mixture which can be intermittent or 
continuous is allowed to flow through the bed of adsorbent which is 
adsorbing hydrocarbons for as long as the monitored hydrocarbon 
concentration in the vented substantially hydrocarbon-free air is below a 
preselected concentration. During that time and after the bed of adsorbent 
being regenerated has been subjected to regeneration for at least a normal 
cycle time, the liquid seal vacuum pump 70, the booster pump 152 and the 
liquid absorbent pumps 112 and 122 are shut-down to conserve power. 
Referring now to FIG. 3, an alternate apparatus for carrying out the 
improved high efficiency process of the present invention is illustrated 
and generally designated by the numeral 170. The apparatus 170 is 
identical to the apparatus 150 illustrated in FIG. 2 and described above 
except that an air cooler 172 is substituted for the cooler 108, a 
hydrocarbon condenser 174 is substituted for the absorber 102, a single 
condensed hydrocarbon pump 182 is substituted for the two liquid absorbent 
pumps 112 and 122, an air cooler 186 is utilized to cool condensed 
hydrocarbons withdrawn from the accumulator compartment 82 of the vessel 
78, a portion of the cooled condensed hydrocarbons is circulated to the 
hydrocarbon condenser by a conduit 184 and a portion of the cooled 
condensed hydrocarbons is conducted to storage by a conduit 188. 
OPERATION OF THE APATUS 170 
Referring to FIG. 3 wherein the same character references as used in FIG. 2 
refer to the same parts as those shown in FIG. 2, the operation of the 
apparatus 170 is identical to the operation of the apparatus 150 described 
above except for the operation of the hydrocarbon condenser 176, the pump 
182 and the air coolers 172 and 186. While the hydrocarbon condenser and 
related equipment is illustrated in FIG. 3 as a part of a high efficiency 
process and apparatus, it will be understood by those skilled in the art 
that the hydrocarbon condenser and related equipment can also be 
substituted in the process and apparatus of FIG. 1. 
The operation of the liquid seal vacuum pump 70, the three-phase separator 
compartment 80 of the vessel 78 and the accumulator compartment 82 of the 
vessel 78 are the same as described above in connection with the apparatus 
10 and 150. Instead of being cooled by a cooler (heat exchanger) 108, the 
seal liquid flowing through the conduit 106 from the three-phase separator 
compartment 80 to the inlet connection 72 of the liquid seal vacuum pump 
70 is cooled by an air cooler 172. 
When the hydrocarbons contained in the inlet air-hydrocarbon vapor mixture 
are readily condensed and separated, a condensing process and apparatus 
can be used instead of a liquid absorbent process and apparatus. That is, 
condensed hydrocarbons conducted from the accumulator compartment 82 of 
the vessel 78 are pumped by the pump 182 by way of the conduit 183 through 
the air cooler 186 whereby the condensed hydrocarbons are cooled. A first 
portion of the cooled condensed hydrocarbons are conducted by the conduit 
184 to the upper portion of the condenser 174. A second portion of the 
cooled condensed hydrocarbons are conducted to storage (not shown) by the 
conduit 188. The air-hydrocarbon vapor mixture separated in the separator 
compartment 80 which flows into the accumulator compartment 82 flows 
upwardly through the hydrocarbon condenser 174 and is intimately contacted 
in a packed section 176 thereof by the downwardly flowing cooled condensed 
hydrocarbon liquid. This causes a major portion of the hydrocarbon vapor 
contained in the upwardly flowing mixture to be condensed and separated 
from the mixture. The separated condensed hydrocarbon liquid passes into 
the accumulator compartment 82 where it mixes with other condensed 
hydrocarbon liquids therein and from where it is removed by way of the 
outlet connection 100, the conduit 110 and the pump 182. The remaining 
mixture of air and hydrocarbon vapor exits the condenser 174 by way of an 
outlet connection 178 therein and is conducted by the conduit 166 to the 
header 124 as previously described. 
Thus, the present invention is well adapted to carry out the objects and 
advantages mentioned as well as those which are inherent therein. While 
numerous changes may be made to the invention by those skilled in the art, 
such changes are encompassed within the spirit of the invention as defined 
by the appended claims.