Abstrict An apparatus for flamelessly reconcentrating liquid desiccant includes
upper and lower enclosed reboiler drums having an enclosed heating
section interposed therebetween. Water-rich liquid desiccant is
continuously recirculated between the upper and lower reboiler drums
through riser conduits disposed within the heating section and return
conduits exterior thereof. Simultaneously with the recirculation
of the water-rich liquid desiccant an exhaust gas stream from a
prime mover is passed through the heating section to convectionally
heat the liquid desiccant within the riser conduits causing disengagement
of water vapors therefrom. The upper drum includes an outlet for
the disengaged water vapors and also an outlet for the resultant
water-lean liquid desiccant.
Claims What is claimed is:
1. 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 for
substantially reconcentrated hot water-lean liquid desiccant, said
means to receive remote from said second outlet;
an enclosed lower reboiler chamber;
a plurality of open-ended riser conduits located essentially 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
circulation 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 only, said heating section having an inlet and
an outlet for exhaust gas flowing from said prime mover transversely
across said riser conduit, whereby liquid desiccant flowing by convection
within said riser conduit from said lower chamber, to said upper
drum is indirectly heated by said exhaust gas to disengage water,
as vapor therefrom; said vapor eventually passing through said first
outlet.
2. An apparatus as in claim 1 including:
a distillation column disposed over said disengaged water vapor
outlet; said distillation column having a stripping and rectifying
portion for intermingling downwardly flowing water-rich liquid desiccant
with said upwardly rising disengaged water vapors; said distillation
column further including an outlet vent for said water vapors; and
a hold back weir adjacent said means to receive having an upper
edge at a higher level than the upper edge of said level control
weir and being positioned within said upper reboiler drum so that
means to receive forms a reservoir for receiving said water-rich
liquid desiccant flowing downwardly from said distillation column;
said reservoir being in fluid communication with said lower reboiler
chamber via at least one of said downcomers.
3. An apparatus as in claim 1 including:
a multiplicity of fins transversely received on said riser conduit
along the longitudinal length thereof for increasing the heat transfer
area thereof.
4. An apparatus as in claim 1 including vapor caps disposed over
the upper end of each of said riser conduits to direct percolating
liquid desiccant down into said main section of said upper reboiler
drum.
Description BACKGROUND OF THE INVENTION
Liquid desiccants such as diethylene glycol or triethylene glycol,
which may be subsequently referred to simply as glycol, have been
widely accepted and are presently being used for dehydrating natural
gas streams. The dehydration occurs by the intimate mixing of the
gas stream with the liquid desiccant and the removal of water from
the gas stream because of the greater affinity of water for the
glycol than 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 off 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 combustion
type prime movers such as piston driven engines or gas fired turbines
which utilize hydrocarbon fluids as fuel. All of these engines produce
fairly high temperature exhaust gases, usually in the range from
700.degree. to 1300.degree. F. which when exhausted directly to
atmosphere represent the loss of amount of recoverable energy in
the form of 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 a method
and apparatus for flamelessly reconcentrating liquid desiccant through
utilization of heat energy produced by an exhaust gas stream emanating
from a prime mover.
SUMMARY OF THE INVENTION
Liquid desiccant is continually recirculated between enclosed upper
and lower drums through riser and return conduits. The riser conduits
are disposed within an enclosed heating section through which a
stream of hot exhaust gases passes to convectionally heat the liquid
desiccant within the riser conduits. Water vapor disengaged by the
heating is removed through an outlet in the upper drum and the resultant
water-lean desiccant is removed therefrom through a second outlet.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of the apparatus of the invention.
FIG. 2 is an end view of the apparatus.
FIG. 3 is a cross-sectional view of the apparatus taken along line
3--3 of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Looking now at FIG. 1 of the drawing, the apparatus of this invention
comprises an enclosed vessel 10 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 central 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. Also included in upper reboiler 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.
The lower drum 14 is an enclosed rectangular structure having an
inlet for water-rich desiccant which fluidly communicates with the
liquid-holding chamber 20 through conduit 32.
Turning now to FIG. 3 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 plate 36 which separates the heating section
and the upper reboiler drum. To 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. Central chamber 18 and bottom drum 14 are further interconnected
by return conduits 40 which pass therebetween exterior of the heating
section and whose upper ends are disposed within drum 12 at a level
lower than the upper end of the riser conduits.
Looking now at FIG. 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 inlet an
exhaust gas outlet 44 to which is affixed an exhaust stack 46. A
butterfly control valve 48 situated within the exhaust stack serves
as a damper to control the volume of exhaust gas flow through the
heating section and in turn is controlled by a temperature sensing
element appropriately mounted in central reboiler 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 distributing the hot exhaust gas stream uniformly
around the length of the riser conduits.
Received 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 the 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 one end of which communicates
with the water-lean dessicant outlet 30 through conduit 66. At the
opposite end of the surge tank is a water-lean dessicant exit connection
68 for returning water-lean dessicant to an external gas dehydration
system. The inlet of the heat exchanger coil 62 is connected by
conduit 70 to the outlet of the reflux condenser section 54 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 of 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 surge tank 58. The water-rich liquid dessicant 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 downwardly through conduit
32 into bottom drum 14. The liquid desiccant then proceeds to and
rises upwardly in the finned riser conduits 34 where heat is 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 14 through the return conduits
40 and up through the riser conduits 34 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 from 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 desiccant is
continuously displaced from the main reboiler section 18 over level
control weir 26 and exits from the upper drum 12 through conduit
66 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. In this
manner heat is exchanged between the cool, water-rich, glycol within
the coil and the hot, water-lean, desiccant in the surge tank. The
water-lean liquid dessicant 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 gases 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 of the stream. Due to the heat differential
between the hot exhaust gases and the water-rich liquid desiccant,
heat is transferred to the desiccant within the riser conduits by
convection over the finned metal surfaces and then by conduction
and convection to the liquid desiccant inside the riser conduits.
After 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. |