Note: Descriptions are shown in the official language in which they were submitted.
~ WO96/36419PCT~S96104~16
-~1, q36~7
METHOD FOR PRECONDITIONING ADSORBENT
AND PRECONDITIONED ADSORBENT
Technical Field
The present invention relates generally to the art
of recovering volatile liquids from air-volatile liquid
vapor mixtures and, more particularly, to an adsorbent
that has been preconditioned for vapor recovery prior to
charging a reaction vessel of a vapor recovery system
with the adsorbent.
Backqround of the Invention
When handling volatile liquids such as hydrocarbons
including gasoline and kerosene, air volatile liquid
vapor mixtures are readily produced. The venting of such
air-vapor mixtures directly into the atmosphere results
in significant pollution of the environment and a fire or
explosion hazard. Accordingly, existing environmental
regulations require the control of such emissions.
As a consequence, a number of processes and
apparatus have been developed and utilized to recover
volatile liquids from air-volatile liquid vapor mixtures.
Generally, the removed volatile liquids are liquefied and
recombined with the volatile liquid from which they were
vaporized thereby making the recovery process more
economical.
The initial vapor recovery systems utilized in the
United States in the late 1920's and early 1930's
21 93~1
WO96/~419 I~ ,'C:'IC
incorporated a process combining compresslon and
r~n~ncation Such systems were originally only utilized
on gasoline storage tanks. It wasn~t until the 1950's
that local air pollution regulations began to be adopted
forcing the installation of vapor recovery systems at
truck loading terminals. Shortly thereafter, the "clean
air~' legislation activity of the 1960's, which culminated
in the Clean Air Act of 1968, further focused nationwide
attention on the gasoline vapor recovery problem. As a
result a lean oil/absorption system was developed. This
system dominated the marketplace for a short time.
Subsequently, in the late 1960's and early 1970's
cryogenic refrigeration systems began gaining market
acceptance ~note, for example, U.S. patent 3,266,262 to
Moragne1. While reliable, cryogenic systems suffer from
a number of shortcomings including high horsepower
requirements. Further, such systems require relatively
rigorous and expensive maintenance to function properly.
Mechanical refrigeration systems also have practical
limits with respect to the amount of cold that may be
delivered, accordingly, the efficiency and capacity of
such systems is limited. In contrast, liquid nitrogen
cooling systems provide more cooling than is required and
are prohibitively expensive to operate for this type of
2~ application.
As a result of these cryogenic refrigeration system
shortcomings, alternative technology was sought and
adsorptior./absorption vapor recovery systems were more
recently developed. one such sy~tem is disclosed in, for
example, U.S.Patent 4,066,423 to McGill et al. Such
systems utilize a bed of solid adsorbent selected, for
example, from silica gel, certain forms of porous mineral
such as alumina and --gn~ql~, and most preferably
activated charcoal or carbon. These adsorbents have an
~WO96/36419 2 1~ 3 ,~ 1~ 7 r~ c.~c ~l6
affinity for volatile hydrocarbon liquids. Thus, as the
air-hydrocarbon vapor mixture is passed through the bed,
a major portion of the hydrocarbons contained in the
mixture are adsorbed on the bed. The resulting residue
gas stream comprising substantially hydrocarbon-free air
is well within regulated allowable emission levels and is
exhausted into the environment.
During the adsorption process, the adsorbent
increases significantly in temperature. This is due to
the release of the heat of adsorption of hydrocarbon and
also side exothermic reactions with impurities contained
in the air-hydrocarbon vapor mixture being processed. As
a result of these factors, undesired and potentially
unsafe overheating may occur under certain operating
conditions. In order to better prevent such overheating
of the beds of adsorbent, it is well known to establish
a residual heel of hydrocarbons in the adsorbent prior to
conducting vapor recovery processing.
In the past, this "preconditioning" of the adsorbent
has been completed ~on-site~ in the actual vapor recovery
system. Specifically, new/clean adsorbent is charged
into the reaction vessel. The reaction vessel is then
sealed and a vacuum is est~hl;sh~. Nitrogen is then
delivered to the reaction vessel to provide an inert
atmosphere and aasoline vapor and nitrogen are then
circulated throuah the reaction vessel and, therefore,
the adsorbent in the bed of the reaction vessel for an
extended period of time. During this gasoline vapor -
nitrogen circulation, the adsorbent heats up due to the
~30 release of the heat of adsorption. Once the desired heel
is established, however, the adsorbent normally cools
~down to near ambient temperature. After the
establishment of ehe resid~al heel is verified, the vapor
recovery system is ready to be returned to normal field
~09C~36419 ~ 9.~6&7 PCT~S9~104~16
operation.
It, of course, should be appreciated that as this
preconditioning process is performed the vapor recovery
system is out of service. Accordingly, the system is
unable to provide any emission control and, therefore,
the terminal loading operation is also out of service.
Due to the diificulty and uncertainty of preconditioning
adsorber.t, the preconditioning process generally takes at
least 30 hours to complete and may even take up to one
hundred hours in extreme conditions. As large loading
terminal operations may generate revenue of up to $3
million per 2~ hour period, it should be appreciated that
any shut down for the preconditioning of the adsorber.t
leads to a substantial loss of revenue. Further, the
rerouting or rescheduling of terminal loading activity
through other terminal locations is troublesome, time
consuming and costly A need, therefore, is clearly
identified for an improved method for changing the
adsorbent in the reaction vessel beds of a vapor recovery
system that significantly reduces the downtime of the
vapor recovery system and, therefore, the downtime of the
loading terminal.
Summarv of tr.e Invention
Accordingly, it is a primary object of the presert
invention to provide an adsorbent that has been
preconditioned for vapor recovery prior to adding to the
vapor recovery system so as to substantially reduce
system downtime and thereby minimize loss of revenue as
well as srhe~ ng and routing complications.
Stated another way, it is an object of the present
invention to provide a preconditioned adsorbent for
096~64lg ~5~ 3 b 3 7 PCI~Sg6/04516
charging a reaction vessel of a vapor recovery system.
Advantageously, such a preconditioned adsorbent
significantly reduces vapor recovery system downtime
- while also allowing one to better predict total downtime
for purposes of precise scheduling and routing.
Additional objects, advantages and other novel
features of the invention will be set forth in part in
the description that follows and in part will become
apparent to those skilled in the art upon examination of
the following or may be learned with the practice of the
invention. The objects and advantages of the invention
may be realized and obtained by means of the
inStLI - tAl ities and combinations particularly pointed
out in the appended claims.
To achieve the foregoing and other objects, and in
accordance with the purposes of the present invention as
described herein, a method is provided for
preconditioning an adsorbent prior to charging a reaction
vessel of a vapor recovery system with the adsorbent.
Preferably, the method includes the steps of (1) treating
the adsorbent to establish in the adsorbent a residual
heel of vapor of the type to be adsorbed in subsequent
vapor recovery processing and (2) adding the treated and,
therefore, preconditioned adsorbent to the reaction
vessel of the vapor recovery system. In this way, it is
possible to ready the vapor recovery system for vapor
recovery processing without any further "on-site"
conditloning of the adsorbent. Accordingly, the vapor
recovery system no longer is required to be shut down for
30 to 100 hours to condition the adsorbent. As a result,
when changing adsorbent overall downtime of the vapor
recovery system is significantly reduced.
Advantageously, this leads directly to substantial
revenue gains for the terminal operator.
W096/3~1~ 2 ~ u 8 ~ PCT/US46~16
More specifically describing the invention, the
treating step includes the fillLng of an adsorber vessel
with adsorbent, and then the sealing of the adsorber
vessel. Next is the evacuating of the adsorber vessel
to, for example, 27 inches of mercury vacuum. This is
followed by the adding of nitrogen to the adsorber vessel
and the circulating of a gasoline vapor and nitrogen
mixture through the adsorber vessel and the adsorbent
until a residual heel of vapor is established in the
adsorbent. The fully preconditioned adsorbent is then
removed from the adsorber vessel. It is stored in air
tight and water tight vessels such as ~OT drums in order
to prevent contamination and loss of "conditioning~.
Thus, the a~sAlrhAnt remains ready to be shipped to an end
l~ user. The preconditioned adsorbent is then simply added
to the reaction vessel of the vapor recovery system which
is then immediately ready for operation and terminal
loadiny.
Still other objects of the present invention will
become apparent to those skilled in this art from the
following description wherein there is shown and
described a preferred r~ho~;r~nt of this invention,
simply by way of illustration of one of the modes best
suited to carry out the invention. As it will be
2~ realized, the invention is capable of other different
embn~;r~nt~ and its several details are capable of
modification in various, obvious aspects all without
departing from the invention. Accordingly, the drawings
and descriptions will be regarded as illustrative in
nature and not as restrictive.
~ WO96/36~19 2 ~ ~ 3 h ~ 7 PCT~S9610J~16
Brief DescriDtion of the Drawinq
The accompanying drawing incorporated in and forming
a part of the specification, illustrates several aspects
of the present invention and together with the
description serves to explain the principles of the
invention. In the drawing:
Figure 1 is a side elevational schematic
representation of a processing apparatus for the
preconditioning of an adsorbent in accordance with the
method of the present invention.
Reference will now be made in detail to the present
preferred embodiment of the invention, an example of
which is illustrated in the ~c~pAnying drawing.
Detailed DescriDtion of the Invention
Reference is now made to Figure 1 showing one form
of apparatus 10 that may be utilized to complete the
method for preconditioning adsorbent such as activated
carbons or charcoal prior to the charging of a reaction
vessel of a vapor recovery system with the adsorbent. As
shown, the apparatus lO includes an adsorber vessel 12
~e.g. 600 ft3 capacity~ connected via conduits 14 and 16
to a packed column absorber 18. A series of flow control
valves 20, 22, 24, and 26 and a service conduit 28 allow
the flow of fluid through the adsorber vessel 12 to be
selectively reversed relative to the packed column
absorber 18 as desired during preconditioning.
Referring now to the method of the present
invention, the method includes the initial step of
treating the adsorbent to establish in the adsorbent a
residual heel of vapor of a type to be adsorbed in
WO96/36419 ~¦ -,J 3 i~ 8 7 ~ ~'CL'16
subse~uent vapor recovery processing. In the method
being described, activated carbon adsorbent is being
treated with hydrocarbon vapor. It should be
appreciated, however, that this adsorbent and vapor are
selected for purposes of illustration only and this
invention is not to be considered as limited
thereto.
This treating is completed by first filling the
adsorber treatment vessel 12 with the activated carbon.
More specifically, the hatch 30 is opened and the
adsorber vessel 12 is filled, for example, to the seam
line 32 formed between the side wall 34 and head 36 ~e.g.
filled with approximately ll,000 lbs of activated
carbon). The activated carbon is spread away from the
fill hatch 30 and leveled as much as possible. The hatch
30 is then repositioned over the fill opening. As this
is done, all activated carbon is removed from the flange
around of the fill opening to insure that a good air
tight seal is established.
At this point, the activated carbon has not been
exposed to hydrocarbon vapor levels in any appreciable
amounts. The initial saturation with hydrocarbon vapors
is accomplished by utilizing recycled hydrocarbon vapors
from the packed column absorber l3 in a nitrogen
atmosphere. The inert r.itrogen atmosphere is necessary
to reduce the risk of overheating the bed of activated
carbon and thereby minimize the ha7ards associated
therewith. More specifically, during initial saturation
heat is released rapidly during the adsorption of
hydrocarbons on the new activated carbon. Thus, it
should be appreciated that the temperature of the
activated carbon in the adsorber vessel 12 is monitored
closely during processing. The temperature rise occurs
as a "wave front" as the hydrocarbon vapor adsorption
~ W096l36419 2 ! 9 3 6 ~3 7 rcTnsg6l04~l6
zone works its way up .hrough the bed of activated
carbon. Temperatures as high as 200~F are commonly
observed along this wave front.
Following the filling and sealing of the adsorber
vessel 12, is the step of evacuating the adsorber vessel.
More specifically, the sparger valves 38, 40 and 42 and
vacuum control valve 44 are all opened. The port of
valve 44 is then connected to a vacuum pump 48. With the
flow control valves 20, 22, 24 and 26 as well as adsorber
vessel drain valve 50 all closed vacuum pump 48 is
operated to establish a vacuum of, for example, 27 inches
of mercury vacuum in the absorber vessel 12. once
established, the vacuum control valve 44 is closed. The
vacuum in the adsorber vessel 12 is then monitored for a
short period of time to insure that there are no air
leaks. If a leak is discovered, the leak is identified
and a proper seal is established. The steps just
described are then repeated to establish the 27 inches of
mercury vacuum in the adsorber vessel 12.
Next is the adding oE nitrogen to the adsorber
vessel 12. More specifically, the port of control
valve 44 is now connected to a source of nitrogen 52. A
regulator on the nitrogen source S2 is set for 100-125
psig and the control valve 44 is opened. This allows
nitrogen to begin to bleed into the adsorber vessel 12.
The delivery of nitrogen to the adsorber vessel 12
continues through the control valve 44 until the vacuum
gage 54 reads 0 vacuum (e.g. until approximately 650 ft3
of nitrogen are delivered) . The port of control valve 44
is then reconnected to the vacuum pump 48 and a vacuum is
again drawn down to 27 inches of mercury vacuum in the
adsorber vessel 12. Nitrogen is then reintroduced into
the adsorber vessel 12 for a second time in the manner
previously described until the vacuum gage 54 reads 0
WO96l36~19 2 ~ q 3 r~ 8 7 PCT~S9610~16
vacuum. h 27 inches of mercury vacuum is then
reestablished in the adsorber vessel 12 for a third time
in the manner previously described. Nitrogen is then
introduced into the ~c~rh~r vessel 12 for a third time
also in the manner previously described until the vacuum
gage 54 again reads 0 vacuum. At this time the control
valve 44 is closed and this portion of the procedure for
establishing an inert atmosphere in the adsorber vessel
12 is completed.
Now the blower 56 and packed column absorber 18 are
purged by nitrogen to displace as much air as possible.
specifically, the nitrogen source 52 is conneoted to the
port of valve 58 and valves 58 and 60 are opened 50 that
nitrogen flows through the blower 56 and the packed
column absorber 18. Once purging is completed, the
valves 58 and 60 are closed.
Next, the packed column absorber 18 is filled
with fresh gasoline to a predetermined level (e.g. with
approximately 100 gallons~. Specifically, a source of
gasoline 62 is connected to the port of valve 64: valve
64 being opened to allow the delivery of gasoline to the
packed column absorber 18. When filling is completed,
the valve 64 is closed.
Next, valves 22 and 26 are opened and blower S6 and
gasoline pump 66 are activated and gasoline is sprayed
into the packed column absorber 18 by means of the
sprayer 67 As a result, gasoline vapors are circulated
in a predominately inert nitrogen atmosphere from the
packed column absorber 18 to the adsorber vessel 12 (and
the ac~.ivated carbon cont~in~d therein) and back again in
a closed loop through the conduits 14, 16 This
circulating step is continued for, approximately, 15 to
hours. During this time should the said vapor
pressure of the gasoline fall below a particular level
WO96/36419 2 1 3 3 ~ 7 PCT~596/045l6
(e.g. 8 RVP) it may be necessary to inject liquid butane
into the lean gasoline in the packed column absorber 18.
This is done through the port connected to the valve 68.
As the gasoline vapor is circulated through the
saturation loop from the packed column absorber 18
through the conduit 14, the adsorber vessel 12 and back
through the conduit 16, vapor is adsorbed by the
activated carbor. in an adsorption zone that gradually
rises upwardly in the adsorber vessel 12. The sparger
valves 38, 40, 42 equally distribute the gas flow so that
all the carbon is relatively equally preconditioned.
After the activated carbon is saturated with
hydrocarbon, the activated carbon begins to cool. At
this time, the direction of flow ~s reversed. This is
accomplished by closing the valves 22 and 26 and opening
the valves 20 and 24. Circulation of gasoline vapor is
then continued in the reverse direction through the
adsorber vessel 12 for 15 to 50 hours. At the end of 30-
100 hours when all temperatures measured along the height
of the adsorber vessel 12 are below 100~F, the blower
pump 56 and gasoline pump 66 are deactivated and gasoline
vapor circulation in the apparatus 10 is terminated.
Next, the hatch 30 of the adsorber vessel 12 is
carefully opened to allow venting to atmosphere and a
sample of preconditioned carbon is carefully removed from
the adsorber vessel. This sample is weighted to insure
that a proper gasoline heel has been established. If
not, the nitrogen atmosphere is reestablished and the
saturation loop just described ~whereir. gasoline vapor
~ 30 flows between the packed column absorber 18 and the
adsorber vessel 12) is reinitiated until the proper heel
~ weight has been established.
Once this is done, the next step in quality control
is to purge the entire system wi.th air and restart the
W0~6~3641~ 3 ~ ~3 7 PCT~S96/0~516
saturation loop. If the carbon vessel temperatures
remain steady, the saturation process is complete. If
the temperatures do not remain below 100~F, the
saturation loop i6 continued until all temperatures are
again below 100~F.
After saturation i6 completed, valves 20, 22, 24 and
26 are closed and pump 66 and blower 56 are again
deactivated. The carbon vessel fill hatch 30 is then
opened. Further, the valve 60 may be open to atmosphere
to alleviate any system pressure. Next, valve 50 is
opened to drain the preconditioned activated carbon from
the vessel 12. The preconditioned carbon may be
collect.ed in an air tight and water tight drum for
shipping to the end user if desired.
Following shipping, is the adding of the treated and
preconditioned activated carbon to the reaction vessel of
the vapor recovery system of the customer.
Advantageously, as a result of the off~site
preconditioning process just described, the vapor
recovery system is made substantially immediately ready
for vapor recovery processing. ~o furtner
preconditioning of the activated carbon needs to be
completed l'on-site" in the vapor recovery system as this
has already been done. Consequently, the 30 to lO0 hours
normally necessary to complete this preconditioning are
not required and the terminal loading facility equipped
with the vapor recovery system may be put into service
sooner without this substantial additional shut downtime.
As a result, revenue losses due to downtime are
significantly reduced.
It should further be appreciated that in some cas~s,
the prior art approach of non-site~ conditioning of _he
activated carbon in the vapor recovery ~ystem can lead to
further significant complications. For example, in
~ WO96/3~1'9 2 1 ~ 3 ~ ~ 7 PCT~S9610~16
certain situations, the activated carbon may not cool
down properly so that gasoline loading may resume. In
these instances, it may be necessary to flood the
reaction vessel with water to achieve the rec~uired
cooling. When this is done, the activated carbon cannot
effectively adsorb hydror~rh~n~ for up to six weeks.
Therefore, the associated loading terminal is only able
to cperate out of EPA compliance and may possibly need to
be shut down for the entire period. By preconditioning
off site in the manner described in the present
invention, this potential problem is completely avoided.
In summary, numerous benefits result from employing
the concepts of the preaent invention. The present
method for preconditioning an adsorbent off site in a
lS controlled situation serves to significantly reduce the
cost, downtime, and uncertainty associated with the rior
art method of conditioning the carbon "on-site" after it
is charged into the reaction vessel of the vapor recovery
system. The end user is effectively provided with a
large economic benefit as vapor recovery system downtime
is reduced by up to 30-l00 hours. Accordingly, 30 to l00
hours of revenue generation are restored to the terminal
operator.
The foregoing description of a preferred embodiment
2~ of the invention has been presented for purposes of
illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form
disclosed. Obvious modifications or variations are
possible in light of the above t~rh; nrJ5 . For example,
an air cooler or chiller 70 may be used in combir,ation
with a heat exchanger 72 to remove heat from the
nitrogen/gasoline vapor mixture circulating through the
closed saturation loop during preconditioning of the
activated carbon. The ~mho~;r-nt was chosen and
W096/~419 ~jl 9 3 6 ~ 7 PCTIUS'J6~16
14
described to provide the best illustration oi the
principles of the invention and its practical application
to thereby enable one of ordinary skill in the art to
utilize the invention in various ~mho~im~nts and with
S various modlfications as are suited to the particular use
contemplated. All such modifications and variations are
within the scope of the invention as determined by the
appended claims when interpreted in accordance with the
breadth to which they are fairly, legally and equitably
entitled.
