Note: Descriptions are shown in the official language in which they were submitted.
CRYOGEMIC HEATER
BACKGROUND OF THE INVENTION
lo Field of the Invention
This invention relates to a device for heating a con-
fined fluid medium and is particularly related to heating
cryogenic fluids, such as liquified petroleum gas to convert
it from the liquid to the gas state.
2. Description of the Prior Art
In the past, cryogenic liquids have been heated using
natural draft radiant heaters. This type heater has several
drawbacks primarily due to the problem of attaining suffi-
ciènt heat transfer when the source of heat is in radiant
form. In most cryogenic applications the process tubes are
below the freezing point and a layer of ice is formed on the
tubes. Ice is a very poor heat conductor. Thus, the radiant
type heater is seldom used at the present time in cryogenic
applications.
Convective heaters have been utilized which transfer heat
by flowing tempered products of combustion over a bank of
processing tubes (usually finned tubes) through which the
cryogenic liquid is circulated. The convective heaters are
usually of -the fan recirculation, jet recirculation, or
excess air type. These type heaters have proved more suc-
cessful than the radiant type; however, each has certain
disadvantages and are relatively expensive.
A submerged exhaust heater has been employed in which the
hot products of combustion are bubbled throu~h water to
cxeate a froth. ~eat transfer tubes carrying the cryogenic
fluid are submersed in the water. There are two basic pro-
blems with the submerged exhaust type heater, that is: (1)
the direct contact between the products and water results in
contamination of water causing it to become acidic; and
~2) since the combustion has to overcome the water head,
this type heater usually requires high blower horsepower
compared to the other types of heating systems.
The type of heater which has proven most successful is
the indirect water vat heater. A burner is fired into a
tube immersed in a bath of water. Process coils are immersed
in the same bath above the fire tube. The heated wa-ter rises
~,
s~
to the top and transfers heat by natural convection to the
process tubes carrying the cryogenic liquids. While this
heater has proven successful, designs up to the present
time have not achieved a high level of energy transfer
e~ficiency and, in fact, the typical unit has a thermal
efficiency of about 70~.
~ It is an object of this invention to provide an im-
proved heater for heating cryogenic liquids such as liqui-
fied petroleum gas (LPG). This invention is directed to-
wards an improvement in the indirect water bath heaterand has the advantages of the water bath heater in that
the flue gas is confined to the fire tube. The process
flow coils are immerséd in the water bath and are never
contacted by the flue gas. In addition to these basic
advantages, the present invention is a substantial improve-
ment over the state of the art in that thermal efficiencies
of as high as 95% can be attained. In these times of high
eneryy cost and the importance of fuel conservation, the
present invention is significant in achieving reduced energy
consumption.
I A more particular object of this inven-tion is to pro-
vide an apparatus for heating a cryogenic liquid such as
LPG in a manner wherein the heat transfer efficiency, or
thermal efficiency, is greatly improved over e~istin~ type
heaters.
These general objects as well as other and more specific
objects of the invention will be fulfilled in the following
description and claims, taken in conjunction with the at-
tached drawings.
3536
S~MMARY OF THE INVENTION
Accord.ing to the invention there is provided an
apparatus for heating a confined liquid medium comprising:
a closed vessel having a heat transfer liquid
therein;
a burner housing within said vessel at least
substantially submerged to said heat transfer liquid;
a burner having a fuel inlet and combustion air inlet,
the burner having a flame outlet communicating with the
interior of said burner housing;
a flue conduit connected to said burner housing at a
point spaced from said burner flame outlet, the flue conduit
extending sealably through the vessel wall and communicating
with the atmosphere;
a liquid medium heat exchanger in the form of at
least one elongated horizontal conduit supported within the
upper portion of said vessel externally of said burner housing
including inlet and outlet conduits passing sealably through
the wall oE said vessel;
a transfer liquid heat exchanger within said burner
housing intermediate said burner flame outlet and said flue
conduit, including at least one inlet and outlet passing
sealably through the wall of said burner housing including
means of circulating the heat transfer liquid therethrough;
a pump havi.ng an inlet and outlet, the inlet having
communication with said vessel; and
a spargin~ tube positioned adjacent, parallel to,
and below the liquid medium heat exchanger, the sparging tube
being in the form of at least one elongated horizontal perfor-
ated tube and being connected to receive and discharge -the flow
of heat transfer medium from said pump.
--3--
~3~31~
DESCRIPTION OF THE DRAWINGS
FIGURE l is an elevational cross-sectional view of a
heatex for a confined liquid medium such as LPG wherein
the heater is in the form of a horizontal vessel having a
burner at one end.
FIGURE 2 is a cross-sectional view taken along the
line 2-2 of FIGURE 1.
FIGURE 3 is a cross-sectional view taken along the
line 3-3 of FIGURE 1.
FIGURE 4 is an elevational cross-sectional view, shown
broken away in the center to reduce the illustrated length
thereof. FIGURE 4 shows an alternate arrangement of the
invention and provides means wherein the transfer liquid
heat exchanger utilizes natural convection.
FIGURE 5 is a cross-sectional view of the alternate
embodiment taken along the line 5-5 of FIGURE 4.
3~:~3~i
DEI'AILED DESCRIPTION
Referrlng to the drawings and first to FIGURES 1, 2
and 3, a preferred embodiment of the invention is illus-
trated. The heater includes a closed vessel 10. In the
illustrated arrangement vessel 10 is of a horizontal con-
figuration, that is, it is cylindrical with the cylindrical
axis being horizontal, the vessel being supported on members
12. The vessel 10 has end walls 10A and 10B. Supported on
the first end wall 10A is a burner 14 which has an air in-
let 16 and a fuel inlet 18. An opening 10C is formed in
housing 10. Within burner 14 fuel and gas are mixed and
the combustion of the gas is directed into the interior of
the vessel 10. Within the vessel a burner housing 20 is
placed. The housing 20 is cylindrical and has one end wall
20A which is coincident with the vessel end wall 10A. At
the opposite end wall 20B of the burner housing there is
an opening 20C which communicates with a flue chamber 22.
Connected to the flue chamber is a flue conduit 24 which
extends sealably through an opening 10D in vessel 10. The
heat of combustion from burner 14 thus heats the interior
of the burner housing 20 and the gases of combustion pass
through the flue chamber 22 and out the flue conduit 24 to
the atmosphere.
Positioned within the flue chamber 22 is a transfer
liquid heat exchanger generally indicated by the numeral 26
which is in the form of looped finned tubes. Positioned
above the burner housing 20 is a horizontal perforated
sparging tube 28. The sparging tube is connected in series
with the transfer liquid heat exchanger 26.
The interior of vessel 10 is filled with a heat trans-
fer medium 30 such as water. In order to extract maximum
heat .from the combustion of fuel, water is withdrawn through
a pipe 32 connected to the lower end of vessel 10 and by
means of a pump 3~ the water is recycled through pipe 36
which connects with the transfer liquid heat exchanger 26.
The recycled water passes through the heat exchanger 26
and is discharged through outlets in sparging tube 28.
Positioned in the upper portion of the interior of
vessel 10 is a liquid medium heat exchanger generally
3~3~
indicated by the numeral 38. In the illustrated embodiment
the liquid medium heat exchanger 38 is in the form of hori-
zontally disposed finned tubes 40 which pass out through
the vessel end wall lOB. The liquid medium to be heated
which, as previously indicated, may be a cryogenic liquid
such as liquified petroleum gas (LPG), is passed through
the length of the finned tube 40 and out of the vessel.
The liquid to be heated is at all times confined within
the liquid medium heat exchanger 38 and there is no contact
of this liquid medium with the heat transfer medium 30
within the vessel. In like manner, there is no contact
between the combustion gases confined within the burner
housing 20 and the liquid medium heat exchanger 38. A11
of the transfer of heat from combustion within the combus-
tion housing 20 to the liquid medium heat exchanger 38takes place by transfer through the heat transfer medium
30, which as previously indicated, is preferably in the
form o water. The heat transfer medium 30 is heated by
the large area of contact with the burner housing 20, the
flue chamber 22, and the flue conduit 24. In addition, any
heat of combustion which is not absorbed in the burner hous-
ing 20 is utilized to provide heat exchange by transfer
liquid heat exchanger 26 as the flue gas is passed there-
through on the way to flue conduit 24. This substantia].ly
increases the thermal efficiency of the unit and, in
practical application, a thermal efficiency as high as 95
has been attained.
To further increase the heat transfer from the heat
of combustion to the cryogenic liquids flowing through the
liquid medium heat exchanger 38, -the circulation of water
by pump 34 extracts heat rom the transfer liquid heat -
exchanger 26 and delivers it out through sparging tube 38.
This circulation of water and delivery through the per-
forated sparging tube causes turbulence around the liquid
medium heat exchanger 38. Furtherl with proper operating
parameters, the heat transfer medium water delivered by
pump 34 can be controlled at a rate such that in the trans-
er liquid heat exchanger 26 the water is at least partially
converted to steam. Thls steam is discharged through
perforated sparging tube 28 to further cause agitation of
the water around the liquid medium heat exchanger 38 and
even further increase the effectiveness of heat transfer
from the liquid medium to the cryogenic fluid flowing
through the finned tubes 40. Chilled liquid such as LPG
absoxbs heat as it flows through the heat exchanger 38 and
is transformed from a liquid to a gas. The gas passes out
and is thereby usable as a gaseous fuel which does not have
to be stored at low temperatures. Thus the heater performs
the objective of the invention as set forth, that is, it
provides a means of heating a cryogenic liquid in a manner
wherein the efficiency o~ heat transfer of the fuel of
combustion to the cxyogenic liquid is greatly increased.
Further, the heater of this invention has the advantage
that all of the heat transfer takes place by means of the
liquid medium 30. There is no contact of the products of
combustion with the heat transfer medium 30, so it is not
contaminated and therefore does not have to be replaced
nor chemically treated.
3~i3~;
ALTERNATE ~BODIMENT
Referring to FIGURES 4 and 5l an alternate arrangement
of the invention is shown. The invention is essentially
the same as that described with reference to FIGURES 1, 2
and 3 except for the difference in the arrangement of the
transfer liquid heat exchanger. In the alternate arrange-
ment the heat transfer medium 30 is induced to flow through
the transfer liquid heat exchanger 26A by natural convection
rather than by use of a pump as in the first described
embodiment. For this purpose, the transfer liquid heat
exchanger 26A is in the form of a plurality of finned tubes
42 which are arranged vertically within the flue chamber
22. Each of the finned tubes 42 communicates through an
opening at the top and bottom of the flue chamber so that
liquid medium 30 is free to pass upwardly through the tubes
42. As flue gas flows past the heat exchanger 26A, heating
tubes 42, this heat is transferred to the water therein,
causing the heated water to rise and thus inducing natural
convection.
As an additional alternate arrangement, outlet pipe
36A from pump 34 may be connected directly to sparging tube
28A, Pump 34 circulates heat transfer medium from the
interior of the vessel 1`0 and discharges it beneath the
liquid medium heat exchamger 38. This causes turbulence
to increase the effectiveness of heat transfer to the
cryogenic liquids flowing into the heat exchan~er 38.
Both embodiments of the invention as set forth herein
achieve highly improved thermal efficiency by providing a
maximum extraction of the heat available from the com-
bustion of gas in the burner housing 20. A substantial
portion of any heat remaining which would othe.rwise pass
out to the atmosphere through the flue conduit 24 is ex-
tracted in the transfer liquid heat exchanger 26 or 26A
and conducted to the heat transfer medium 30.
While the inven-tion has been described with a certain
degree of particularity, it is manifest that many changes
may be made in the details of construction and the arrange-
ment of components without departing from the spirit and
scope of this disclosure. It is understood that -the
~IL~L9~S36i
invention is not limited to the embodiment set forth herein
for purposes of exemplification, but is to be limited only
by the scope of the attached claim or claims, including
the full range of equivalency to which each element or
S step thereof is entitled.
