Note: Descriptions are shown in the official language in which they were submitted.
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Liquid desiccants such as di.ethylene glycol or
triethylene glycol, which may be subsequen-tly referred
to simply as glycol, have been widely accepted and are
presently being used ~or dehydrat:Lng natural gas streams.
The dehydration occurs by the intimate mixing of the
yas stream with the li.quid desiccant and the removal
of water from the gas stream because of the greater
affinity of water for the glycol t:han the gas stream.
The resultant moisture laden or water-rich glycol
then must be dehydrated itself. Presently this dehydration
of the glycol is accomplished by heating or reboiling
the liquid above its boiling point so that the water is
driven o~f and water-lean glycol is collected to be
recycled to the contact zone of the natural gas stream.
A fire tube having an open flame is usually utilized
to heat the water~laden glycol. In many situations the
use of an open flame presents a problem due to the fire
danger inherent to the use thereof. One situation occurs
on off-shore platforms which are many miles from any fire
fighting equipment and hence requires that all fire hazards
be reduced to a minimum.
Most gas gathering systems have included therein
internal comhustion type prime movers such as piston driven
engines or gas fired turbines which utilize hydrocarbon
: fluids as fuel. A11 of these engines p.roduce fairly high
temperature exhaust gases, usually in the range from 700
to 1300 F. which when exhausted directly to atmosphere
represent the loss oE amount of recoverable energy in the
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form ot` heat. Such losses have heretofore been considered to be largely
unavoidable and in only isolated instances have efforts been extended to
recover this energy.
It is therefore an object of this invention to present an apparatus
for flamelessly reconcentrating liquid desiccant through utilization oF heat
energy produced by an exhaust gas stream emanating from a prime mover.
According to the present i.nvention ther~ is provided a reboiler for
reconcentrating liquid desiccant through utilization of exhaust gas from a
prime mover comprising: an enclosed upper reboiler drum having means to
receive water-rich-desiccant, a first outlet for disengaged water vapors and
a second outlet ~or substantially reconcentrated hot water-lean liquid desic-
cant, said means to receive remote from said second outlet; an enclosed lower
reboiler chamber; a plurality of open-ended riser conduits located essential-
ly between said means to receive and said second outlet each conduit having
one end communicating with the interior of said lower reboiler chamber and
having the other end protruding upwardly into said upper drum wherethrough
liquid desiccant flows upwardly from said lower reboiler chamber into said
upper reboiler drum; at least one downcomer having one end communicating with
the interior of said upper reboiler drum and with the other end communicating
with the interior of said lower reboiler chamber to provide downward circula-
tion of~water-rich-liquid desiccant to said lower chamber as said desiccant
moves to said second outlet; a liquid level control weir positioned within
said upper reboiler drum adjacent said second outlet to provide overflow of
water-lean desiccant to said second outlet; and an enclosed heating section,
said heating section being disposed between said upper drum and lower reboiler
chamber and enveloping said riser conduit onlyj said heating section having
an m let~and an outlet for exhaust gas flowing from said prime mover trans-
versely across said riser conduit, whereby liquid desiccant flowing by convec-
tion within said riser conduit from said lower chamber to said upper drum is
30~ indirectly heated by said exhaust gas to disengage wa~er, as vapor therefrom;
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said vapor eventually passlng through sa:id first outlet.
In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
Figure 1 is a side view of an apparatus according to the invention.
Figure 2 is an end view of the apparatus.
Figure 3 is a cross-sectional view of the apparatus taken along
line 3-3 of Figure l.
Looking now at Figure 1 of the clrawing, the apparatus comprises
an enclosed vessel lO having three main sections, an upper reboiler drum 12,
a bottom drum 14, and an enclosed heating section 16 disposed therebetween.
Upper reboiler drum 12 is subdivided into a cen~ral
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chamber 18, a liquid-holding chamber 20, and a water-lean
desiccant chamber 22 by a liquid hold-back weir 24 and
a liquid level control weir 26 appropriately disposed
within the drum. The upper edge of liquid level control
weir 26 is lower than the upper edge of liquid hold-back
weir 28. ~lso included in upper reobiler drum 12 is an
outlet for disengaged water vapors 28 and an outlet for
water-lean desiccant 30, the utility of which will become
evident in the subsequent description.
~ rrhe lower drum 14 is an enclosed rectangular
structure having an inlet for water-rich desiccant which
fluidly communicates with the liquid-holding chamber
20 throuyh conduit 32.
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Turning now to FIGURE ~, it can be seen that the
lower drum 14 is interconnected to the central chamber of
the upper drum by means of a plurality of open~ended
riser conduits 34 which pass through the heating section 16
and protrude upwardly into central chamber 18. The riser
conduits are appropriately sealed at the transversement
thereof through a divider place 36 which separates the
heating section and the upper reboiler drum. ~o increase
the magnitude of heat transfer, riser conduits 34 have
received on the outer surface thereof a plurality of
transverse juxtaposed fins of relative thin sheet stock.
Positioned over the upper ends of each of the riser conduits
are vapor caps 38. ~entral chamber 18 and bottom drum 14
are further intexconnected by return conduits 40 which
pass therebetween exterior of the heating section and whose
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upper ends are disposed within drum 12 at a level lower
than the upper end of -the riser conduits.
Looking now at FIGURE 1 again, the heater section
16 encloses the riser conduits and embodies an inlet 42
for an exhaust gas stream received from a prime mover
(not shown) and opposite the inlel: an exhaust gas outlet 44 to
which is affixed an exhaust stack 46. A butterfly control
; valve 46 situated within the exhaust stack serves as a
damper to control the volume o~ exhaust gas flow through
the heating section and in turn is controlled by a kemperature
sensing element appropriately mounted in central ~eboiler
chamber 18. The butterfly control valve and associated
temperature sensing element may require a bypass of all or
part of the exhaust gas stream around the heating section.
Such bypassing systems are commonly known in the industry
and can be easily installed by one skilled in the art.
Within the heating section adjacent inlet 42 is at least
one diverter baffle 43 for distributin~ the hot exhaust
gas stream uniformly around the length of the riser
conduits.
Recieved over the disengaged water vapor outlet and
secured to the reboiler drum is an upstanding elongated ~ -
~; cylindrical distillation column 50 which embraces a
vapor vent 52, a reflux condenser 54 section having an
inlet and outlet, and a packed or tray section 56.
Directly below t~e bottom drum 14 is a surge tank 58
which rests upon feet 60 and which has disposed therein a
heat exchange coil 62. The surge tank includes an inlet 64,
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one end of which communicates with the water-lean desiccant
; outlet 30 through conduit 66. At the opposite end of the
surge tank is a water-lean desiccant exit connection 6
for returning water-lean desiccant to an external yas
dehydration system. The inlet of the heat exchanger coil
~ 62 is connected by conduit 70 to the outlet of the reflux
; condenser section 5~ and the outlet thereof is connected
by conduit 72 to the distillation column 50 at a point
above a portion of the trayed section 56 such that desiccant
flowing therein is discharged within the column over a
portion o~ the trays.
The vessel 10 has received thereover a blanket of
. insulation 74 to retain the heat therein and consequently
to increase the efficiency of the apparatus.
In operation, cool water-rich liquid desiccant 76
such as glycol, returning from an external process
dehydration system enters the regeneration system at the
inlet to the reflux condenser section 54 in the top of the
distillation column 50. The liquid desiccant exits
therefrom within conduit 70 and proceeds to enter and flow
through heat exchanger coil 62 where the water-rich
liquid desiccant receives heat from hot, water-lean,
: desiccant flowing countercurrently in the surg~ tank 5~.
The water-rich liquid desiccant progresses from the heat
exchanger coil through conduit 72 into the distillation
column where it flows downwardly through a portion of the
trayed section 56 and enters the liquid-holding chamber 20
in the upper reboiler drum 12, from whence it proceeds
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downwardly throu~h conduit 32 into bottom drum 1~. The
liquid desiccant then proceeds to and rises upwardly in
the finned riser conduits 34 where heat i5 transferred
thereto from a hot exhaust gas stream 78 in the heating
section 16 until it is expelled from the upper end of
the riser conduits into the main reboiler section 18.
Within the main reboiler section a natural convection
type reboiling action takes place. That is, a portion of
the desiccant is continually recirculated back to the
bottom drum 1~ through the return conduits 40 and up through
the riser conduits 3~ back into the main reboiler section
where the liquid desiccant enters as a partial vapor and
partial liquid stream. The vapor caps 38 installed over
each of the riser conduits directs percolating liquid
desiccant back down into the main reboiler section.
The water vapors disengaged from the liquid desiccant
at the top of the riser conduit 34 ascend upwardly ~rom
the main reboiler section into the distillation column and
pass through the trayed and reflux condenser sections
thereof where a portion of the vapors are condensed to
liquid reflux and the remaining vapors are vented to
atmosphere through vent 52.
A stream of hot, water-lean, reconcentrated liquid
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desiccant is continuously displaced from the main reboiler
section 18 over level control weir 26 and exits from the
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upper drum 12 through conduit 86 into surge tank 58,
where the hot lean desiccant flows past the heating coil
in a direction countercurrent to that of the flow of
the cool, water-rich, liquid desiccant within the coil.
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; In this manner heat is exchanged be-tween the cool, water-
rich, glycol within the coil and the hot, water-lean
desiccant in the surge tank. The water-lean liquid
desiccant then exits from the regeneration system and
returns to the external gas processing dehydration system.
Simultaneous with the heretofore discussed flow of
the liquid desiccant, the stream of hot exhaust yases 78
coming from a prime mover enters the heating section 16 at
the inlet thereof and is distributed around the outside
of the finned riser conduits 34 by the diverter baffle 43
and the natural turbulence o~ the stream. Due to the
heat differential between the hot exhaust gases and the
water-rich liquid desiccant, heat is transferred to the
desiccant withïn the riser conduits by convection over the
finned metal surfaces and then by conduction and convection
to the liquid desiccant inside the riser conduits. ~fter
giving up a portion of the heat, the exhaust gas stream
proceeds to the atmosphere through the stack 46. As
previously mentioned the temperature of the liquid desiccant
is controlled by regulating the volume of flow of the hot
gas stream by a temperature sensor located within the main
reboiler section 18 which activates a butterfly control
damper valve located within the exhaust stack.
During the description of the preferred embodiments
specific language has been used for the sake of clarity.
However, it is to be understood that the words used are not
words of limitation and include all words which operate in a
similar manner to accomplish a similar purpose.
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