Note: Descriptions are shown in the official language in which they were submitted.
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AIR RECUPERATOR C~EANE~
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BACKGROUND OF THE INVENTION
This invention relates in general to a method and
apparatus for cleaning air recuperators and, in particular,
to an on-line method and apparatus for air recuperator cleaning.
More specifically, but ~"ithout restriction to the
particular use which is shown and described, this invention
relates to a method and apparatus for on-line cleaning of
finely-divided carbon black p`owder deposits from gas-to-gas
tube and shell recuperators.
In the production of carbon black or other highly
dispersed, high-surface activity solids formed by pyrogellic
processes, the solids are transported by a gas stream for
ultimate deposition in flexible tube filters or similar dcvices.
Before depositing the solids material on or in such filters,
it is desirable -to remove the heat from the transporting was
for reuse in the system. Therefore, the heat from such trans-
port gas is generally removed by heat exchangers which include
bundles of tubes through which -the transport gas and carton
black solids material is passing. As the carbon black is carried
through the tubes by the transport gas, deposits of carbon black
particles form on the internal walls of the tubes. Thesc dcposits
reduce both the flow of the transport gas through the tubs, and
the efficient transfer of heat from the gas. In particularly
aggravated situations, a complete blockage of an individual
tube can occur which may lead to damage of the heat exchanger.
Since -the ends of the tube are secured in a tube sheet, a tube
in which the carbon build-up has caused a blockage becomes
cooler than the adjacent tubes through which the hot transport
gas is being passed. As a result, the cooler tube produces
contraction stresses on the tube sheet which can tear the blocked
tube free from its moun-ting in the tube sheet.
In an attempt to resolve this problem, some heat
exchangers are designed such that the decrease in heat transfer
efficiency is attempted Jo be compensated for by increasing the
heat exchange surface area thereby oversizing the apparatus
for the needs of the process. However, such oversizing is a
temporary solution to the problem. As the unit is in service,
deposits and subsequent fouling will eventually occur, decreasing
the system efficiency and resulting in a decrease below process
requirements.
Various methods and apparatus have been utilized to
clean carbon black deposits :from the tube interiors such as
chemical treatment with or without mechanical scrubbing. How-
ever, chemical me-thods require that -the unit be taken o~f-line
and out of production, as well as requiring expert handling of
the chemicals to prevent damage to the metal parts of the heat
exchanger. The varlous mechanical cleaning methods wh:ich llave
been utilized require a large amount of manual labor, sigh as
by forcing a long worm or wire brush through each tubc, or
sandblasting.
Accordingl~V, different attempts have been made to
prevent such excessive build-up by utilizing cleaning jut
nozzles such as disclosed in U.S. Pa-tents Nos. 2,069,57~;
3,364,~83; 4,141,754; and 4,366,003. Each of the systems
disclosed in these patents utilizes a discharge of high
pressure air from jet nozzles positioned over an inlet
opening to the tube in order to provide a short burst oE
a cleaning gas into the processing tubes. While such systems
may be somewhat satisfactory, they increase the mechanical
complexity of the overall system, and necessitate added
controls and maintenance costs.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to
improve the method and apparatus for cleaning air recuperators
by removing built-up carbon deposits from the inner surfaces
of a transporter tube through which the carbon black particles
are transpor-ted when extracting heat from the transport was.
Another object of thls invention is to prevent
excessive build-up or blockage of the transport tube due to
the accumulation of finely--dispersed, high surface activity
solids transported in -the gas s-tream through the transport
tubes.
A further object of this invention is to prevcnt
excessive build-up of carbon black. particles on the intcrior
walls of a heat exchange transpor-ter tube through an on-line
system which does not require that the heat exchanger ye taken
off-line in order to prevent such excessive build-up.
Still another object of this invention is to clean
finely-divided inorganic powder deposits from gas-to-gas
tube and shell recuperators without interrupting the operation
of the heat exchanger or utilizing chemical cleaning processes
or expensive, maintenance-requiring mechanical cleaning
systems.
These and other objects are attained in accordance
with the present invention wherein there is provided a method
and apparatus for interrupting the flow of carbon black
particle-carrying transport gas passing through recuperator
tubes for a short period of -time to cause the carbon hlack
material accumulating and adhering to the inner walls of the
tube to be removed therefrorn and swept from the tube by the
resumption of transporter gas flow.
ESCRIPTION OF THE DRAWINGS
Further objects of the inven-tion together with
additional features contributing thereto and advantages
accruing therefrom will be apparent from the following
description of a preferred embodiment of the invention
which is shown in the accompanying drawings with like
reference numera].s indicating corresponding parts -throu~]h-
out, wherein;
FIG. 1 is a fron-tal perspective view of a gas to-
gas shell and tube recuperator apparatus utilizing the
invention;
FIG. 2 is a horizontal planar view of the top of
recuperator apparatus such as illustrated in FIG. 1 with
portions broken away to illustrate components of the
invention;
` FIG. 3 is a partial sectional view of the apparatus
shown in FIG. 2 taken along lines 3--3;
FIG. is a par-tial sec-tional view of the apparatus
shown in FIG. 2 taken along lines 4-~;
FIG. 5 is a horizon-tal p]anar view of a portion of
the apparatus of the invention;
FIG. 6 is a horizontal planar view of a por-tion of
the invention to better illustrate the components thereof;
FIG. 7 is a cross-sectional view of -the structure
shown in FIG. 6 -taken along lines 7-7; and
FIG. 8 is an enlarged illustration of a portion of
the invention to bet-ter illustrate the details thereof.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to FIG. 1, there is illustrated a
gas-to-gas shell and tube recuperator 100 having a plurality
of individual recuperator tubes 10 secured in a tube sheet 12
and through which a carbon black particle carrying transport gas
is passed. The tubes 10 are enclosed by a shell 20 into which
a heat exchanging medium or transfer gas is introduced through
an inlet 21 to remove and transfer the heat from the trc~l~sport
gas for further use. The heat transfer gas passes within the
shell 20 and out through a discharge outlet, not shown, to remove
heat from the transfer gas passing through the tubes 10.
As previously discussed, during the transport of the
carbon black particles through the tubes 10, the interior
surface of the tubes accumulates carbon black particles.
This ac`cumulation interferes with the efficient transfer of
heat from the transport gas to the heat transfer medium being
circulated through the recuperator shell 20, and may even-tually
clog the tube interior which can result in a tube 10 pulling
loose from the tube sheet 12 in which it is secured. There-
fore, a shutter or flow interrupter assembly 50 is positioned
adjacent to a discharge end 11 of the tubes 10, to provide
a system for removing the carbon black build-up within the
tube interior.
The shutter assembly 50 includes a shutter or slide
plate 51 formed in three sections 51A, 51B, and 51C, all three
of which function in the same manner and, except for the diff-
erences in shape, are structurally the same. Therefore, for
c'onvenience of illus-tration, these shutter plates will be
referred to by the general reference numeral 51.
s shown in FIG. 2, the shutter plates 51 are supported
adjacent the discharge end 11 of -the recuperator tubes 10
and are formed with a series of holes or apertures 52 corres-
pending in number and size to the adjacent discharge opening 11
of the tubes 10. In this manner the carbon black particle-
carrying transport gas will pass through the holes 52 wormed
in the shutter pla-te 51 for further processing. The skitter or
slide plate 51, shown in planar view in FIG. 5, also has a
plurality of guide slots 53 formed longitudinally in the
shutter plate 51 between adjacent rows of apertures 52 to assist
in guiding the sliding movement of the shutter plate.
Each of the shutter or slide plates 51 is secured at
one end to a push rod 60 which is appropriately journaled
61 in a flange portion 22 of the recuperator shell 20 to
permit sliding movement of the shutter plate 51 in a direc-tion
transverse to the longitudinal axis of the recuperator tubes 10.
The length of travel of the push rod 60 and the length of the
guide slots 53 can function to limit the sliding plate move-
Kent. The push rod 60 may be spring-loaded to return to an
initial, unbiased position wherein the apertures 52 formed in
the slide or shutter plate 51 are coaxially aligned with the
discharge opening 11 of the recuperator tubes 10 and out of
interference with the flow of carbon black particle-carrying
transport gas. In addition,~the pins 60 may be connected to
a suitable apparatus, not shown, which will impart a quick
sliding movement to the shutter plates 51 to move the plate
into and out from interference with the flow of the transport
gas through the recuperator tubes 10 as desired.
As best shown in FIGS. 3-8, the shutter plate 51 is
supported adjacent to, or in sliding contact with, the discharge
end 11 of the recuperator tubes 10 such that the pl.ate ma
slide into a position to block the dissha.rge end 11 of the
recuperator tubes 10. Support plates 55 are cut to conform to
the outer peripheral surface of the recuperator tubes 10, and
are welded near the discharge end 11 khereof Oll-t of interEerence
with the flow of the transport gas therethrough. plurcllity of
vertically extendiny guide pins 56 are welded to the face of the
- lZ~2186
support plates 55. The guide pins 56 extend outwardly a
distance sufficient to pass through the guide slots 53 of
the shutter plate 51. Upon positioning of the shutter plate
with the guide pins 56 extending through the guide slots
formed therein, a corresponding plurality of washers 57 are
tack--welded to the protruding end of the guide pins 56 to hold
the slide or shutter plates 51 in proper alignment when moved
transversely into and out from blocking the flow of the transport
gas through the recuperator tubes 10. In this manner, the
transverse sliding movement of the shutter plates 51 into
and out from blocking the discharge from the recuperator
tubes 10 will be guided and controlled.
The movement of the slide or shutter plates 51 across
the discharge ends 11 of the recuperator tubes 10 is preferably
done very quickly, and suddenly, for a short time period such
as on the order of one-second duration. The more sudden and
complete the blockage of the discharge end 11 of the tubes,
the Gore beneficial the effect in dislodging the carbon particle
build-up from the tube interior. The frequency of blocking
the transport gas flow in order to maintain acceptable recup-
erator performance varies with the type of finely-divided powder
being produced, but is believed to generally range from one
to sixty cycles per hour. While it is not known with certainty
as to what causes this dislodgement, it is believed that the
coating dislodgement occurs through three basic mechanisms:
1. A water hammer effect and concomitant pressure
wave which travels down the tube causing rapid compression and
expansion of the transport gas in the recuperator tube, thus
mechanically breaking or dislodging some of the carbon deposits
By
from the tube interior.
2. The sudden blockage of the tube results in the
recuperator tube cooling for a fraction of a second, such
that the resultant differential expansion of the processing
tube and the internal carbon black particle coatinc3 weakcns
the binding of the carbon black particles to the tube intcrior.
3. The sudden stoppage of the -transport gas flow
results in the cessation of an electric curren-t being generated
by movement of the finely-divided particles carried in the
-transport gas stream. This electrostatic charge which is
generated by this movement is imparted -to the individual carbon
black particles eausing them -to adhere to the interior wall
ox the tubes. Interruption of the flow of the transport gas
permits this electrostatic charge to be dissipated througil the
metal walls of the tubes at a rate faster than the eharc3e is
being accumulated, thus reducing or eliminating some of the
electrostatie attraetive forces which are believed to create,
in part, the accumulation of the carbon black particles.
While the invention has been described in the speci-
fication and illustrated in the drawings with reference to apreferred embodiment, it will be understood by those skillcd in
the art that various changes may be made and equivalen-ts may be
substitued for elements thereof without departing from thc scope
of the invention. In addition, many modifications may be made
to adapt a particular situa-tion or material to the tcac}linc~s of
the invention without departing from the essential scope thereof.
Therefore, it is intended -that the invention not be limitL~d to the
particular embodiment illustrated by -the drawings alld clescriL~cd
~2~
in the specification as the best mode presently contemplated
for carrying out this invention, bu-t that the invention will
include any embodiments falling within the scope of the
appended claims.
