A method and apparatus for cleaning a heat exchanger during operation thereof. The heat exchanger includes a plurality of tubes through which a first fluid is conducted from an inlet end to an outlet end in indirect heat transfer relationship with a second fluid disposed on the outside of the tubes intermediate the inlet and outlet ends of the tubes. Further, the heat exchanger includes an inlet chamber for the first fluid communicating with the inlet ends of the tubes, and a tube sheet for supporting the inlet ends of the tubes and isolating the inlet chamber from the second fluid, the inlet ends of the tubes extending into the inlet chamber beyond the tube sheet. The method of cleaning comprises introducing a particulate cleaning media between the inlet ends of the tubes and the tube sheet, and then forcing the introduced particulate cleaning media in a direction counter to the direction of flow of the first fluid through the tubes along the exterior surfaces of the tubes to the inlet ends of the tubes so that the particulate cleaning media is introduced into the tubes and is directed against the inner walls thereof as the flow of particulate cleaning media is changed so that it flows through the tubes in the direction of the flow of the first fluid. Apparatus is also disclosed for cleaning of a heat exchanger in accordance with this method.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for self-cleaning 
of heat exchangers of the shell-tube type in which transfer of heat is 
effected between two media, one of the media being conveyed through sets 
of tubes connected in parallel and the other media passing through the 
space between the tubes. More particularly, the present invention relates 
to a method and apparatus for cleaning the inner walls of the tubes of 
such shell-tube type heat exchangers. 
As is well known to persons skilled in the art, the efficiency of a heat 
exchanger of the shell-tube type is unavoidably lessened after some time 
of operation due to deposits on the tube walls, especially to deposits 
along the inner tube walls. Such deposits may be caused by mechanical 
impurities carried by the media flowing through the tubes which condense 
along the tube walls or by substances contained in the media in a state of 
solution but percipitated therefrom by thermal and/or chemical influences. 
These deposits impede the heat transition to transfer through the tube 
walls and thereby deteriorate the efficiency of the heat exchanger. When 
this efficiency is lowered to a certain fraction of the original 
efficiency thereof, the tubes have to be cleaned mechanically and/or 
chemically to restore the original efficiency. As can be appreciated, 
having to take the heat exchanger out of operation to accomplish this 
cleaning necessarily lessens the economic efficiency of the apparatus in 
which the heat exchanger is employed, and thus tends to increase the cost 
of operation of the unit. 
It is desirable in many instances to recover and utilize for a useful 
purpose hot gases generated by combustion or other plant operation which 
might otherwise simply be exhausted to the atmosphere. For example, in 
foundry operations, significant amounts of heat are generated in the 
melting furnace or cupola. It has been found that this heat can be used 
effectively and for a useful purpose as for instance, in heating a second 
fluid, such as water which may then be utilized for space heating of the 
plant. Normally, the hot gases generated in the furnace are directed 
through air pollution and filtering systems for removing entrained ash, 
molten slag or other condensable fumes which necessarily results in a 
cooling of the gases such that it is often not possible to utilize 
efficiently such gases in a heat exchanger. Accordingly, it has been found 
desirable to pass the hot dirty gases through a heat exchanger prior to 
conduction through air pollution and environmental filtering systems. 
However, passing of such dirty gases through tubes in a shell-tube type 
heat exchanger has generally been found to result in significant 
condensation of the condensable fumes and accumulation to the entrained 
ash and molten slag on the inner surfaces of the tubes which, as noted 
above, reduces the heat transfer efficiency of the heat exchanger. 
Because it is desirable to pass the hot dirty gases through the tubes prior 
to air pollution environmental filtering systems, the amount of 
accumulation of deposits on the inner tube walls is necessarily amplified 
and greatly increased over accumulations found in other applications which 
use relatively clean gases. Thus, to provide for efficient operation of 
the plant and in particular of the heat exchanger in which hot dirty gases 
pass, it is found preferable to provide some means for self-cleaning of 
such heat exchangers, either continuously during operation, or 
intermittently, without necessitating a shut down of the heat exchanger. 
In the past, to clean such heavy deposits on the inner tube walls, it has 
been suggested that particulate cleaning media or matter be introduced 
into the inlet chamber for the tubes and to then flow through the tubes to 
scour the inner walls to remove the accumulation of slag and/or condensed 
metal fumes. 
However, introduction of such particulate cleaning matter in the inlet 
chamber causes such particles to become entrained in the hot dirty gases 
which flow at high speeds through the tubes. This results in the major 
portion of the entrained particles flowing through the central portion of 
the tubes because of the flow velocity distribution of the gases through 
the tubes. Further, to the extent that any of the particulate cleaning 
matter is directed against the inner walls of the tubes, such particles 
flow at too high of a velocity which thereby creates erosion of the tube 
surfaces with a consequent wearing out or through of the tubes. Thus, use 
of particulate cleaning particles in the past has not proved efficient for 
cleaning of the inner tube walls in heat recovery systems which utilize 
the flow of hot dirty gases through the tubes of a shell-tube type heat 
exchanger. 
SUMMARY OF THE INVENTION 
These and other disadvantages of the prior art are overcome with the method 
and apparatus of the present invention which is directed to cleaning of a 
heat exchanger during operation in which the heat exchanger has a 
plurality of tubes through which a first fluid is conducted from an inlet 
end to an outlet end in indirect heat transfer relationship with a second 
media disposed on the outside of the tubes intermediate the inlet and 
outlet ends of the tubes, and in which the heat exchanger further includes 
an inlet chamber for the first fluid communicating with the inlet ends of 
the tubes, and a tube sheet for supporting the inlet ends of the tubes and 
for isolating the first fluid in the inlet chamber from the second heat 
transfer media, the inlet ends of the tubes extending into the inlet 
chamber beyond the tube sheet. According to the method of the present 
invention, a particulate cleaning medium is introduced between the inlet 
ends of the tubes and the tube sheet and is then forced in a direction 
counter to the direction of flow of the first fluid through the tubes 
along the exterior surfaces of the tubes to the inlet ends of the tubes so 
that the particulate cleaning matter is introduced into the tubes and is 
directed against the inner walls of the tubes as the direction of flow is 
changed so that the particulate cleaning media flows through the tubes in 
the direction of the flow of the first fluid. In this way, the particulate 
cleaning media does not become entrained in the flow of the first fluid 
through the tubes, but is rather pulled along the inner walls of the tubes 
at a much slower velocity to result in an efficient cleaning of the tubes 
without causing erosion of the tube surfaces. 
According to the apparatus of the present invention, in the shell-tube type 
heat exchanger, means are provided for distributing the particulate 
cleaning media between the inlet ends of the tubes and the tube sheet and 
for forcing the particulate cleaning media along the exterior surfaces of 
the tubes to the inlet ends of the tubes in a direction counter to the 
direction of flow of the fluid through the tubes so that the particulate 
cleaning media is introduced into the tubes and is directed against the 
inner walls of the tubes as its direction of flow is changed and it moves 
in the direction of flow of the fluid through the tubes. 
Preferably, the inlet ends of the tubes are arranged at an elevation above 
the outlet ends of the tubes, and the tube sheet is positioned below the 
inlet ends of the tubes. In this way, the distributing means for the 
particulate forces the particulate cleaning media upwardly along the 
exterior surfaces of the tube to the inlet ends of the tubes, and then 
gravity pulls the particulate matter downwardly along the inner tube 
walls. The fluid flow through the tubes forces the particulate matter 
which falls into the tubes against the side inner walls of the tubes. Yet, 
the particulate matter, in being directed to an elevation just above the 
inlet ends of the tubes, does not become entrained in the fluid flow 
through the tubes which might otherwise deleteriously affect the efficient 
cleaning action of the particulate matter along the inner tube walls which 
has been a problem of the prior art. 
In a further preferred embodiment, the inlet ends of the tubes are funnel 
shaped having a tapered open end tapering to a narrow inner diameter of 
the tubes. Such an arrangement is advantageous to cause the particulate 
cleaning media when introduced into the tubes to be directed against the 
inner walls of the tubes upon downward movement of the particulate 
cleaning matter through the tubes. 
These and other features and characteristics of the present invention will 
be apparent from the following detailed description in which reference is 
made to the enclosed drawings which illustrate a preferred embodiment of 
the present invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings in which like reference numerals represent 
like components, there is shown in FIG. 1 a self-cleaning heat exchanger 
10 constructed in accordance with the present invention. The heat 
exchanger 10 is generally of the shell-tube type in which there are a 
plurality of generally parallel tubes 12 for a first fluid which is 
adapted to flow therethrough in indirect heat transfer relationship with 
respect to a second heat transfer media arranged on the outer surfaces of 
such tubes. In particular, the self-cleaning heat exchanger 10 of the 
present invention is adapted to receive the hot dirty gases generated in a 
industrial plant, such as a foundry furnace or cupola, and to recover and 
utilize for a useful purpose the heat contained in such gases. In such a 
system, the hot dirty gases generated in the industrial plant comprise the 
first fluid which is adapted to flow through the tubes 12. The second heat 
transfer medium is conducted along or around the outer surfaces of such 
tubes 12 intermediate the ends thereof to receive, by indirect heat 
transfer through the walls of the tubes 12, at least a portion of the heat 
contained in the gases. This second heat transfer medium may comprise a 
gas, a liquid, or even solid particulate, such as in the form of pebbles, 
etc., which, when coming in contact with the outer surfaces of the tubes, 
receive a portion of the heat of the hot gases flowing therethrough. Of 
course, it is to be understood that while the present invention will be 
described with reference to such a system wherein hot dirty gases 
generated in an industrial plant comprise the first fluid flowing through 
the tubes, the heat exchange apparatus 10 of the present invention may 
also be used in connection with other types of systems and is not meant to 
be limited solely for use in industrial plants and the like. 
As best seen in FIG. 1, the heat exchanger 10 comprises a generally 
vertically oriented, cylindrically shaped vessel 14 having an inlet 
conduit 16 at its upper end and an outlet conduit 18 at its lower end. 
Inside the vessel 14, the heat exchanger 10 includes an inlet chamber or 
plenum 20 communicating with the inlet conduit 16 for receiving the hot 
dirty gases, heat transfer section or plenum 22 in which the heat of the 
hot dirty gases is transferred to the secondary heat transfer media, and 
an outlet chamber or plenum 24 communicating with the outlet conduit 18 
for receiving the cooled, dirty gases after they have given up a portion 
of their heat in the heat transfer plenum 22. The three plenums are 
defined and separated by upper and lower tube sheets 26, 28 which support 
the upper inlet and lower outer ends 30, 32 of the plurality of tubes 12 
respectively. That is, the upper tube sheet 26 serves to support the upper 
or inlet ends 30 of the tubes 12 and to isolate the inlet chamber 20 
receiving the hot gases from the secondary heat transfer media whereas the 
lower tube sheet 28 serves to support the lower outlet ends 32 of the 
tubes 12 and to isolate the outlet chamber 24 receiving the cooled gases 
from the secondary heat transfer media. The heat transfer plenum or 
section 22 in which the secondary heat transfer media circulate is thus 
defined between the upper and lower tube sheets 26, 28. 
The hot dirty gases generated in the plant are conducted into the inlet 
chamber 20 above the inlet ends 30 of the tubes 12 and then flow 
downwardly through the tubes 12. As the gases pass downwardly inside the 
tubes 12 through the heat transfer plenum 24, some of the heat of the 
gases is given up to the secondary heat transfer media. After passing 
through the heat transfer plenum 24, the cooled gas then flows downwardly 
into the outlet chamber 24. From the outlet chamber 24, the cooled dirty 
gases are conducted through the outlet conduit 18 to air pollution control 
equipment and an exhaust fan (not shown). The exhaust fan serves as a 
driving force for conduction of the gases through the heat exchanger. 
In the preferred embodiment, the secondary heat transfer media comprises 
water which is adapted to be heated by the hot gases and to serve as a 
heating media for space heaters arranged throughout the foundry or other 
type of industrial plant. The secondary water is introduced into the heat 
transfer chamber 22 through a secondary inlet conduit 34. The water is 
then circulated across the tube surfaces picking up the heat given up by 
the gases and conducted upwardly to a secondary outlet conduit 36. From 
there, the heated water is then conducted to a suitable space heating 
system for heating of the plant. 
For certain types of foundry operations, the air pollution control 
equipment is necessary for environmental purposes in order to remove 
entrained ash particles, slag, condensable metal fumes, etc. before 
exhausting the gases into the atmosphere. As noted herein above, it is 
desirable to first pass the hot dirty gases from the cupola through the 
heat exchanger 10 before passing such gases through the air pollution 
control equipment as such filtering equipment also tends to remove the 
heat contained in the gases. On the other hand, as can be appreciated, the 
entrained ash, molten slag, condensable metal fumes, etc. in the gases 
tend to accumulate on the heat transfer tubes if it is first passed 
through the heat exchanger. This causes fouling of the heat transfer tubes 
and thus a loss in thermal transfer efficiency. Consequently, such fouling 
of the heat transfer surfaces tends to reduce the efficiency of the heat 
exchanger and thus results in a higher cost for operation of the plant. 
Prior art systems have suggested the use of utilizing self-cleaning heat 
exchangers which are capable of cleaning the tube surfaces on a continuous 
basis or intermittently during operation of the plant. For example, such 
prior art systems have suggested the use of particulate cleaning or 
scouring media in the form of sand, limestone, steel shot, etc. which flow 
through the tubes along with the hot dirty gases. The function of the 
scouring media is to clean and scour the inside tube surfaces to prevent a 
significant build up of dust particulate and condensable fumes on the tube 
surfaces. 
In the prior art systems, such scouring media was introduced in the inlet 
chamber above the inlet tube ends to become entrained with the dirty gases 
and then to flow downwardly through the tubes therewith. However, because 
of entrainment in the gases which flow through the tubes at a high 
velocity, there is a tendency, because of the flow velocity distribution 
through the tubes to be bell shaped, for the particles to be directed 
inwardly towards the center of the tubes and thereby not perform any 
scouring of the tube surfaces. This is especially true with lighter 
cleaning particulate matter. On the other hand, if heavier particulate 
matter is utilized so that the particulate matter would move along the 
inner tube surfaces, the scouring media tended to move along the tube 
surfaces at high velocity. This has resulted in erosion, with the 
consequent wearing out or through of the tubes, because of the high 
velocity and the abrasive characteristics of the scouring media. As can be 
appreciated, such is entirely unacceptable since it necessitates the 
removal of the heat exchanger from operation in order to repair the tubes. 
The present invention however, overcomes these disadvantages by first 
distributing particulate cleaning matter in the inlet chamber 20 for the 
hot dirty gases on the upper tube sheet 26 below the tube inlet ends 30 
and then forcing such particulate cleaning matter 42 upwardly along the 
outer surfaces 38 of the tubes 12 to the inlet ends 30 of the tubes 12 in 
a direction counter to the direction of flow of the dirty gases. At the 
tube inlet ends 30, the particulate cleaning matter 42 is allowed to fall 
into the tubes 12 and flow downwardly along the inside surfaces 40 by the 
force of gravity to clean and scour such surfaces 40. Because the 
particulate cleaning matter 42 is initially directed in counter flow to 
the hot dirty gases, such particulate matter 42 does not easily become 
entrained in such gases and therefore the problems experienced by the 
prior art are not encountered. That is, because the particles 42 when they 
are introduced into the tubes 12 are not entrained in the first heat 
transfer fluid (i.e., the hot dirty gases), the particulate matter 42 is 
not conducted downwardly along the tube surfaces 40 at a relatively high 
velocity, nor are they directed inwardly toward the center of the tubes 
12. Instead, the particulate cleaning matter 42 is directed outwardly 
against the inner tube walls 40 upon the introduction into the tubes 12, 
and in essence is dragged along by the gases flowing therethrough and/or 
by gravity. Because of this action, the particles 42 move at a much slower 
velocity along the inner tube surfaces 40 and effectively serve to scour 
and clean such tube surfaces 40 without such a highly abrasive and 
destructive quality as was experienced by the high velocity flowing 
particles of the prior art. 
The particulate cleaning matter or media 42 contemplated by the present 
invention includes sand, steel shot, aluminum particles, limestone and 
similar type granular or coarse particles. Preferably, the particles have 
a size ranging between 100 and 1,000 microns. Further, it is to be noted 
that limestone particles also serve to provide a chemical reaction in 
certain instances to prevent acid build up on the tube surfaces 40. 
More particularly, according to the present invention, scouring or 
particulate cleaning media 42 is initially pumped or transported upwardly 
to an elevation above the upper tube sheet 26 supporting the upper ends 31 
of the tubes 12 of the heat exchanger 10. This may be accomplished by 
means of a pneumatic lifting media such as air which forces the dense 
particles 42 upwardly inside a tube or pipe 44 to an external distribution 
chamber 46 located at the exterior of the heat exchanger 10. At the 
distribution chamber 46, the particulate material 42, for example, sand 
particles, is allowed to flow downwardly through a series of secondary 
conduits 48 spaced about the periphery of the heat exchanger 10 to an 
internal segmented distribution chamber 50 arranged about the inner 
periphery of the heat exchanger 10 and slightly spaced about the upper 
tube sheet 26. As best seen in FIGS. 2 and 3, there are six secondary 
conduits 48 which allow the sand to flow into a segmented inner 
distribution chamber 50 defined by the inner walls of the heat exchanger 
vessel 14 and a distribution ring 52 extending upwardly from the upper 
tube sheet 26 and surrounding all of the tubes 12. 
In the preferred embodiment, the distribution ring 52 extends above the 
inlet ends 30 of the tubes 12 and is provided with a plurality of V-shaped 
channels 54 at the upper edge 55 thereof. In essence, the V-shaped 
channels 54 serve as a weir for the particulate cleaning media introduced 
into the inner distribution chamber 50. As the particulate matter is 
introduced into the segmented chamber 50, the level or elevation thereof 
rises and the particulate sand 42 flows through the V-shaped openings 54 
onto the tube sheet 26 and is distributed inwardly around the bases of the 
tube ends 31 extending upwardly above the tube sheet 26. That is, as more 
particulate sand 42 flows through the opening 54 and onto the tube sheet 
26, the sand will be directed and distributed inwardly toward the central 
most tubes 12. As can be appreciated, the greater the number of tubes 12 
there are and thus the greater the area occupied inside of the 
distribution ring 52, it may be necessary to increase the height of the 
tube ends 31 above the tube sheet 26 in order to have the sand or other 
particulate matter flow inwardly to the central most tubes 12. 
After the sand or other particulate matter has been delivered onto the tube 
sheet 26 and has been roughly distributed about the tubes 12 by means of 
the V-shaped weir openings 54, further finer distribution of the sand 
particles 42 about the tube ends 31 is accomplished by blowing air, such 
as through openings 53, into the region directly above the tube sheet 26 
but below the tube inlet ends 30 in order to fluidize the sand or other 
particulate matter 42. For this purpose, the openings 53 communicate with 
chamber 51 between the tube sheet 26 and the segmented distribution 
chamber 50. This fluidizing action tends to evenly distribute the sand 42 
which has flowed onto the tube sheet 26 inside of the distribution ring 
52. In addition, this fluidizing serves to force the sand particles 42 
upwardly off of the tube sheet 26 along the outside surfaces 38 of the 
tubes 12. In essence, the elevation of the sand or other particulate 
matter 42 is increased by the blowing of pressurized air into the region 
between the upper tube sheet and the inlet ends 30 of the tubes 12. 
As the sand or other particulate matter 42 is distributed evenly on the 
upper tube sheet 26 and is directed upwardly along the outside surfaces 38 
of the tubes 12, some of the sand particles will reach an elevation at or 
just above the elevation of the inlet ends 30 of the tubes 12. At this 
elevation, the sand or other particulate matter 42 will simply flow by 
gravity into the tube inlet ends 30 over the upper edges 39 of the tubes 
12. From there, the sand will fall downwardly along the inner surfaces 40 
of the tubes 12 by means of gravity to scour the inside surfaces 40. The 
hot dirty gases flowing into the inlet chamber 20 and then down through 
the tubes 12 will force the particulate cleaning media 42 outwardly 
against the inner walls 40 of the tubes 12 and/or will serve to drag such 
particles 42 downwardly along the inner walls 40 of the tubes 12. However, 
because the particulate cleaning matter 42 does not have an opportunity to 
become entrained in the gas flow, the particulate cleaning matter 42 will 
not flow at the high velocity of the gas through the tubes 12, but instead 
will flow under the influence of gravity and the drag forces exerted by 
the gases flowing through the tubes 12. As a result of the fact that the 
particles 42 do not move at such a relatively high velocity, erosion of 
the inner tube surfaces 40 will not occur; rather, an efficient cleaning 
will result. 
Preferably, the inlet ends 30 for the tubes 12 are flared outwardly to 
assume a bell mouthed configuration. This is shown best in FIG. 4. This 
configuration is advantageous for insuring that the particulate cleaning 
matter 42 is directed onto the inner surfaces 40 of the tubes 12 as it is 
introduced into the tubes 12. As the particulate cleaning matter reaches 
the height of the tube inlet ends 30, and flows onto the flared portion of 
the tubes 12 and is directed inwardly towards the interior of the tubes 
12, the gas flow impinging at the inlet ends 30 will force the particles 
42 against the inner side walls 40 of the tubes 12. In essence, as the 
particles flow over the upper edges 39 of the tubes 12 into the tubes 12, 
they fall onto the inner surface 40 and tend to adhere to that surface 40 
as they fall by gravity or are dragged along by the influence of the gas 
flow through the tubes 12. 
Upon exiting from the tubes 12 in the outlet chamber 24, the gas flow is 
turned and directed upwardly through the outlet conduit 18 where it is 
then conducted to air pollution control equipment and the exhaust fan (not 
shown). A gravitational inertia separator 56 is placed in the outlet 
chamber 24 as shown schematically in FIG. 1 to separate the particulate 
cleaning matter 42 from the cooled dirty gases and for directing such 
particulate cleaning matter 42 downwardly to the bottom of the outlet 
chamber 24. From there, the separated particulate matter is conducted 
through appropriate pipes or chutes 58 to a particulate cleaning media 
storage container 60. The particulate cleaning media storage container 60 
feeds the particulate cleaning media 42 into the pneumatic lift system 62 
which serves to supply the particulate matter 42 to the external 
distribution chamber 46 as described hereinabove. Thus, after cleaning, 
the particulate cleaning media 42 is separated from the cooled gases and 
is recycled for use to clean the inside surfaces 40 of the tubes 12 again. 
The gravitational inertia separator 56 placed in the outlet chamber 24 may 
be of any of the conventional types, as are well known in the art, for 
separating particulate matter which has become entrained in the gas flow. 
Such entrainment may occur as the particulate cleaning matter 42 moves 
downwardly through tubes 12 and/or as a result of falling in the 
relatively open outlet chamber 24 where it has an opportunity to become 
entrained as the gas flow turns and is conducted upwardly through the 
outlet conduit 18 to the air pollution control equipment. The particles 
which do not become entrained also fall downwardly to the lower end of the 
outlet chamber 24 and thus to the media storage container 60. 
Thus, it is seen that the present invention provides an efficient means and 
method for cleaning of the inside surfaces 40 of the tubes 12 of a 
shell-tube type heat exchanger 10 without deleteriously affecting the 
surfaces 40 of the tubes 12, etc. By first introducing and distributing 
particulate cleaning matter 42, such as sand, onto the upper surface of 
the tube sheet 26 below the inlet ends 30 of the tubes 12 through which 
the hot dirty gases flow and then forcing such particulate cleaning matter 
42 in a direction counter to the flow of the gases to the inlet ends 30 of 
the tubes 12, the particulate cleaning media 42 does not become entrained 
in the gas flow but rather simply flows downwardly along the inner 
surfaces 40 of the tubes 12, either by gravity and/or drag forces exerted 
by the gas flow. As such, the particulate cleaning matter 42 serves to 
efficiently and effectively clean the inner surfaces 40 of the tubes 12, 
but not with such an abrasive quality as to cause the tubes to wear out or 
through. 
As such cleaning of the tubes 12 is efficient, it may not be necessary to 
operate the cleaning system on a continuous basis during operation of the 
industrial plant or other apparatus in which the heat exchanger 10 is 
placed. Instead, it may be sufficient to only run such cleaning system 
during a portion of the operation of the heat exchanger 10, such as for 
example five minutes of every hour. In such instances, it is not necessary 
to remove all particulate cleaning media 42 from the inlet chamber 20. 
Rather, the fluidizing air which is injected into the bed of particulate 
matter 42 on the surface of the tube sheet 26 may simply be turned off and 
the pneumatic lifting of the particulate cleaning matter 42 stopped. Then, 
the particulate matter 42 will simply settle in the tube sheet 26 below 
the inlet ends 30 of the tubes 12 ready for a subsequent cleaning of the 
tubes 12 as soon as the fluidizing air is activated. 
It is to be noted that only a single pump or blower 63 is necessary for 
both lifting of the sand and fluidizing the bed of particulate matter 42 
on the surface of the upper tube sheet 26. The single blower 63 could 
include appropriate ducting for conducting the air to both the piping 44 
for lifting or conveying of the particulate matter 42 upwardly, and into 
the inlet chamber 20 through chamber 51 and openings 53 for fluidizing the 
bed of particulate matter 42. The single blower 63 could thus fluidize the 
bed of particulate matter 42 on the tube sheet 26 while at the same time 
particulate matter is delivered to the external distribution chamber 46. 
It is to be noted that it is necessary to fluidize the bed of particulate 
matter 42 on the tube sheet 26 and to also deliver sand to the 
distribution chamber only when it is desired to perform a cleaning 
operation on the tubes 12. Otherwise, the blower 63 may simply be turned 
off. 
Alternatively, if cleaning of the tubes 12 of the heat exchanger 10 is done 
on a regular intermittent basis and if the distribution chamber 46 is 
chosen to be of a suitable size, the single blower 63 may serve to deliver 
all of the sand necessary for the cleaning operation to the distribution 
chamber 46 from where it then falls downwardly into the segmented inner 
distribution chamber 50 and onto the tube sheet 26. By means of a 
flip-flop mechanism (not shown), the air conducted from the blower can 
then be directed to fluidize the bed of particulate matter 42 to perform 
the cleaning operation as previously described. After the fluidized 
particulate matter 42 has been introduced into the inlet ends 30 of the 
tubes 12, the blower 63 can be stopped until the next intermittent 
cleaning operation is to be performed. At that time, the blower 63 can be 
turned on and sand lifted to the external distribution chamber 46 above 
the heat exchanger 10 from where the cleaning operation cycle can be 
repeated. 
It is to be noted that in the preferred embodiment, the tubes 12 are 
arranged vertically within the heat exchanger 10 in order to take 
advantage of the gravity forces on the particulate cleaning matter 42 to 
evenly clean the entire inner surfaces 40 of the tubes 12 with the method 
and apparatus of the present invention. That is, by having the tubes 12 
arranged vertically, the particulate cleaning matter 42 falls by gravity 
into the inlet ends 30 of the tubes 12 and moves downwardly along the 
tubes by the force of gravity, which results in a complete and efficient 
cleaning of the inner tube surfaces 40. However, it is contemplated that 
the present invention can also be utilized where the tubes 12 are not 
arranged vertically but are included at an angle, or even where the outlet 
ends are located above the inlet ends. In such operations, the full 
advantage of gravity influence on the particulate cleaning matter 42 will 
not be able to be taken advantage of, but instead the cleaning will be 
dependent on the particles 42 being dragged along the tube surfaces 40 by 
the gas flow. It is to be noted though that in such instances, the 
particles dragged by the gases are not entrained in the gases and 
therefore do not move at the high velocity of such gases. 
Thus, it is seen that the present invention provides an improved method for 
providing continuous cleaning of the heat exchanger 10 of the shell-tube 
type. In such a heat exchanger 10 in which the tubes 12 extend into a gas 
inlet chamber 20 beyond the tube sheet 26, particulate cleaning matter 42, 
in the form of sand, steel shot, limestone, etc., is introduced between 
the tube inlet ends 30 and the tube sheet 26, and is forced along the 
exterior surfaces 38 of the tubes 12 to the tube inlet ends 30 in a 
direction counter to the directional flow of the gases through the tubes 
12. From there, the particulate cleaning matter 42 is introduced into the 
tubes 12 and flows therealong in the direction of the gas flow to 
efficiently clean the inner surfaces 40 of the tubes 12 without eroding 
such tube surfaces. According to the apparatus of the present invention, 
means are provided for introducing and distributing the sand or other 
particulate cleaning media 42 between the tube sheet 26 and the tube inlet 
ends 30, and for forcing such particulate cleaning media 42 along the 
exterior surfaces 38 of the tubes 12 through the inlet ends 30 of the 
tubes 12 in a direction counter to the flow of the gases through the tubes 
12. 
While the preferred embodiment of the present invention has been shown and 
described, it will be understood that such is merely illustrative and that 
changes may be made without departing from the scope of the invention as 
claimed.