Waste heat recovery

Combustion products containing particulate solids such as carbon black are quenched by indirect heat exchange and the build up of solids deposits on the heat exchange surfaces is minimized or deposits on the heat exchange surfaces are removed by providing a fixed bed of fluidizable particulate solids within the indirect heat exchanger and positioning a shell-tube heat exchanger within the bed of solids with the heat exchange fluid being in the shell side and with the gas stream containing entrained solids such as carbon black passing through the tubes which contain particulate solids. Fluidization of the particulate solids by the gas stream containing carbon black, for example, passing through the tubes cleans or keeps the inner peripheries of the tubes clean.

This invention relates to a method and apparatus for the transfer of heat 
from and to gases containing entrained solids. In accordance with another 
aspect, this invention relates to an improved apparatus comprising a waste 
heat recovery unit containing a fluidized fixed bed of particulate solids 
and a shell-tube heat exchange unit within the bed of particulate solids. 
In another aspect, this invention relates to a method for cleaning the 
inner peripheries of the tubes of an indirect heat exchange zone 
containing carbon deposits which indirect heat exchange zone is used to 
quench the effluent from a carbon black producing reaction zone or 
furnace. 
In a typical furnace black process, a carbonaceous feed is introduced into 
a reactor and contacted with hot combustion gases which elevate the 
temperature of the feed to a temperature sufficiently high to decompose 
the feed to form combustion products containing particulate carbon black. 
Such combustion products are typically at a temperature in the range of 
about 2400.degree. F. to about 2900.degree. F. The combustion products are 
cooled, usually by introducing a quench fluid into the combustion 
products, to form an effluent (sometimes referred to as smoke) containing 
particulate carbon black. The effluent is subsequently separated into a 
gas phase and a particulate carbon black phase by separate means, such as 
a cyclone separator, bag filters, or the like. However, before the 
filtering or separation step, the effluent should be cooled to a 
temperature sufficiently low to prevent damage to the separation means. A 
plurality of cooling steps can be employed. 
It is common practice to initially cool or quench the combustion products 
by injecting directly thereinto quench fluid at one or more points in a 
quench chamber portion of the reactor. Typical quench fluids include 
water, cooled effluent or smoke, and/or off-gas, the off-gas being a 
portion of the gas phase separated from the effluent. The first cooling 
step lowers the temperature of the combustion products to a temperature of 
about 2000.degree. F. or less and preferably between about 1500.degree. F. 
and 2000.degree. F. The first cooling is done to lower the temperature of 
the combustion products to a temperature which can be safely accommodated 
in an indirect heat exchange means and to a temperature below which no 
further production of carbon black occurs. 
A second step of cooling involves the use of a first indirect heat exchange 
means such as a shell-tube exchanger which further lowers the temperature 
of the effluent to a temperature of about 1200.degree. F. or less and 
preferably between about 800.degree. F. and about 1200.degree. F. The thus 
cooled effluent can then be passed to one or more economizers, e.g., 
indirect heat exchangers which are operable for heating air and/or feed to 
be introduced into the reactor. It is also common practice in the art to 
finally cool the effluent by injecting a trim quench fluid into the 
effluent before separating effluent. One problem that has been encountered 
in the use of the shell-tube heat exchanger is that carbon black deposits 
tend to build up. Since carbon black is a good insulator, a thin layer of 
the carbon black will substantially lower the heat transfer rate in the 
indirect heat exchanger. It is, therefore, necessary to clean the indirect 
heat exchanger from time to time in order to maintain a high heat transfer 
rate and adequate operating efficiency. The present invention relates to a 
heat exchanger of the shell and tube type within a fixed bed of 
fluidizable particulate solids whereby the tendency of carbon black build 
up in the tubes is substantially minimized and/or deposits are removed by 
the fluidized solids. 
Accordingly, an object of this invention is to provide an improved process 
for producing carbon black. 
Another object of this invention is to provide an improved process for 
maintaining heat exchange surfaces in a relatively clean condition for the 
quenching of carbon black smoke. 
A further object of this invention is to provide a process for cleaning 
tubes of shell-tube heat exchangers or maintaining tubes substantially 
free of deposits without interrupting the operation to the extent that it 
is not necessary to shut down a carbon black producing process. 
Another object of this invention is to provide an improved waste heat 
recovery apparatus. 
A further object is to provide a method for carrying out heat exchange in a 
fluidized bed operation with gases containing suspended solids. 
Other objects and aspects as well as the several advantages of the 
invention will be apparent to those skilled in the art upon reading the 
specification, the drawings, and the appended claims. 
In accordance with the invention, a method is provided for producing carbon 
black which allows for preventing the build up of deposits and/or cleaning 
of deposits from an indirect heat exchanger without the aforementioned 
problems by providing a fixed fluidized bed of suitable particulate solids 
within the indirect heat exchanger and positioning a shell-tube heat 
exchanger within the bed of solids with the heat exchange fluid being on 
the shell side and with a gas stream containing entrained solids such as 
carbon black passing through the tubes which contain particulate solids. 
In accordance with the instant indirect heat exchanger, heat is transferred 
from a gaseous stream containing entrained solids to the fluidized solids 
and by way of the tubes of the heat exchanger to the shell fluid. In 
addition, the fluidized solids maintain the inner peripheries of the tubes 
substantially freed from deposits to allow efficient heat exchange.

The reference numeral 10 designates generally a carbon black reactor of any 
suitable type. Air is introduced into the reactor 10 by way of conduit 11 
and fuel is introduced into reactor 10 via an inlet 12. A carbonaceous 
feed is introduced into the reactor 10 by way of inlet 13. Air and fuel, 
introduced by way of inlets 11 and 12, respectively, can be combusted 
before introduction into the reactor or combusted within a combustion 
chamber of the reactor. The combustion gases contact the feed from the 
inlet 13 and pyrolize the feed to produce combustion products including 
particulate carbon black. Reactor 10 has the outlet thereof connected in 
flow communication with an indirect heat exchanger 14 by conduit means 15. 
A heat exchanger fluid, such as water, is introduced into, the shell side 7 
of a shell-tube heat exchange section 8 of the heat exchanger 14 by way of 
line 16 and, generally, discharges steam by way of outlet 17. Shell-tube 
heat exchange section 8 is provided with tubes 9 which are in open 
communication with inlet 18 and outlet 19 of heat exchanger 14. Tubes 9 
are positioned within a fixed bed of fluidizable particulate solids 21. 
Reactor 10 effluent containing entrained carbon black in line 15 is 
introduced into heat exchanger 14 through inlet 18 and pass upwardly 
through the bed of particulate solids 21 and tubes 9 and exit through 
outlet 19 into line 20. The reactor effluent is passed through heat 
exchanger 14 under conditions which cause the bed of particulate solids to 
be fluidized and thus maintain the inner peripheries of tubes 9 
substantially freed from carbon black deposits. In addition, the bed of 
particulate solids absorbs heat from the reactor effluent gases and 
transfers the heat to the heat exchange fluid in shell side 7. Heat 
exchange zone 14 is provided with a fixed fluidized bed of suitable 
particulate solids 21 extending from a lower portion of heat exchanger 14 
below the inlet to tubes 9 to above the outlet of tubes 9 forming the tube 
and shell section 8 of the heat exchange unit 14. 
The conduit means 20, includes a heat exchanger 22 for receiving effluent 
which can be used as the heat exchange medium for heating such fluids as 
air, carbonaceous feed, and/or water (for example, water charged at inlet 
16) for use in the carbon black producing process as is known in the art. 
The effluent can be conducted from conduit means 20 via a conduit 23, 
pressured by a blower 24 which is connected in flow communication to 
conduit 23. The blower 24 is connected in flow communication to conduit 
means 25 which conducts the cooled effluent back to reactor 10 for use as 
a quench fluid as is known in the art. 
Separating means 26, which can be a bag filter, is connected in flow 
communication with the conduit means 20 for receiving effluent therefrom. 
The separator means 26 is operable for separating the effluent into an 
off-gas phase portion for discharge via outlet 27 and a flocculent carbon 
black phase portion which is discharged via an outlet conduit means 28. 
The outlet conduit means 28 connects the separator means 26 in flow 
communication to a pelleter 29 as is known in the art. The pelleter 29 is 
operable for forming the flocculent carbon black into pellets. A discharge 
conduit means 30 connects the pelleter 29 in flow communication to a 
screener 31 which is operable for receiving the pellets from pelleter 29 
and separating the pellets according to their size. Pellets of the desired 
size are discharged via discharge conduit means 32 to a dryer 33 for 
subsequent drying as is known in the art. Off-sized pellets are discharged 
from screener 31 via discharge conduit means 34. Dried pellets are 
discharged from the dryer 33 via a discharge conduit means 35, and yielded 
as product via conduit 35'. 
In an alternative embodiment of the invention, carbon black recovered from 
the process can be used as the particulate solids for the fixed fluidized 
bed 49 and 50 in indirect heat exchanger 14 by recycling from filter 26, 
pelleter 29, screener 31 or dryer 33 through solids in such a manner that 
said bed of solids extends from below the inlet, through, and above the 
outlet of the tubes. 
Conduit means 37 is connected in flow communication to inlet 18 of heat 
exchanger 14. This can be accomplished in any number of ways as, for 
example, by conduit means 37 opening into the conduit means 15 or the 
conduit means 37 can open into a portion of the reactor 10 (not shown) as, 
for example, into the throat of the venturi of the reactor 10. A 
combination of such connections can also be utilized. Control valve means 
36 in conduit means 37 is operable for allowing sequential introduction of 
carbon black from a source of carbon black into heat exchanger 14. The 
carbon black introduced into heat exchanger 14 from conduit means 37 can 
be from any suitable source of carbon black either external of the 
apparatus or from the apparatus downstream of separating means 26. 
In accordance with the alternative mode of operation, conduit means 37 is 
connected in flow communication to the carbon black outlet conduit means 
28 for utilizing carbon black from the separator means 26 for introduction 
into heat exchanger 14. Heat exchanger 14 is "cleaned" by fluidized 
solids. In the illustrated structure, the flow of carbon black can be in 
one of several manners depending upon the type or types of carbon black 
desired to be introduced into heat exchanger 14. In the event it is 
desired to use partially agglomerated carbon black, conduit means 37 is 
connected in flow communication to the conduit means 28 via conduit means 
38 which opens into conduit means 28. A control valve 39 is connected to 
conduit means 38 for selectively permitting flow of carbon black from 
conduit means 28 to the conduit means 37. Further, as an optional method 
of operation, water can be introduced into the carbon black in conduit 
means 38 as, for example, through an inlet conduit means 40 in a suitable 
mixer (not shown) in the event it is desired to use wet carbon black as a 
part of the particulate solids within heat exchanger 14. 
Carbon black pellets can also be introduced into heat exchange 14 as part 
of the particulate solids. To accomplish this, a conduit means 41 connects 
conduit means 37 in flow communication to the discharge conduit means 34 
and opens into the conduit means 34 for using off-sized specification 
carbon black pellets. Control valve 42 is connected in conduit means 41 
for selectively permitting the use of off-specification carbon black 
pellets directly from the screener as particulate solids for heat 
exchanger 14. 
Also, carbon black pellets from dryer 33 can be utilized as particulate 
solids in heat exchanger 14. To accomplish this, conduit means 43 connects 
conduit means 37 in flow communication to discharge conduit means 35. A 
control valve 44 is connected in conduit means 43 for selectively 
permitting the use of pellets from dryer 33 as part of the particulate 
solids in heat exchanger 14. Gas 25' from blower 24 can be used to actuate 
injector means 36' for conveying solids to conduit 18. 
Referring now to FIG. 2, carbon black reactor smoke in conduit 15 having 
been quenched to about 2000.degree. F. or less using water and/or recycle 
cooled smoke is quenched charged to heat exchanger 14 containing a 
fluidizable bed of solids, such as sand, alumina, coke, carbon black 
pellets, and the like located above a distribution means or grid 46. A 
shell-tube type heat exchange section 8 having shell side 7 and tube means 
9 is positioned within heat exchanger 14 above grid 46. Water enters the 
shell side at 16 and passes through shell side 7 surrounding tubes 9 and 
produced steam exits the shell at 17. The fluidized bed of solids (heat 
transfer material) extends from above grid 46 at 49 and through the tubes 
9 and above the outlet ends of tubes 9 at 50. 
Reactor smoke in conduit 15 passes upwardly through grid 46 and the fixed 
bed of particulate solids 49 and 50 at a rate sufficient to fluidize the 
bed of solids. The tubes 9 are so sized as to be of sufficient diameter to 
allow recirculation of the solids therethrough. The reactor smoke directly 
interchanges heat with the particulate solids which indirectly interchange 
heat with the water or other heat exchange fluid in shell 7 to produce 
steam. In addition, the above recirculation keeps the inner peripheries of 
the tubes substantially freed of carbon black deposits, affording high 
rate of heat exchange from the tube side (tubes 9) to the shell side 
(shell 7) of the shell-tube heat exchanger section 8. 
A cyclone separator 51 is located in the dilute phase 52 above the fixed 
fluidized bed of solids to prevent the heat exchange solids from exiting 
via conduit 20 with the cooled reactor smoke, which exits at about 
1200.degree. F. and at this temperature can be used in conventional 
indirect heat exchange air preheaters, fuel preheaters, and feedstock 
preheaters of the carbon black operation. The finally cooled smoke is 
passed to conventional means (bag filter, cyclone, sand filter, etc.) as 
described in FIG. 1 to recover the carbon black product therefrom. 
Although the invention has been illustrated above using a fixed fluidized 
bed of sand as the heat exchange solids, other solids such as alumina, 
silica-alumina, coke, or carbon black pellets, and the like, of course, 
can be used. Solids other than carbon black entrained in a gas can be heat 
exchanged with the fluidized solids. For example, various pigments 
entrained in gas can be used. Also, instead of water being in the shell 
side of the heat exchanger, Dowtherm or a hydrocarbon to be converted, for 
example, cracked thermally or preheated, can be used in the shell side of 
the heat exchanger. 
Further, instead of cooling a material entrained in a gas, the system can 
be used to heat a material entrained in a gas with the heating fluid 
passing through the shell side located within the fluidized fixed bed of 
solids. 
SPECIFIC EXAMPLE 
The following calculated example sets forth conditions and particular 
dimensions for an apparatus such as set forth in the drawings. 
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Specific 
Ranges 
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(a) Calculated Example 
(15) Carbon Black Reactor Effluent: 
SCF/hour, 467,500 -- 
Lbs CB/1000 SCF, 6.47 -- 
Temperature, .degree.F. 
2,000 1800-2100 
Pressure, psig, 5 2-30 
(16) Water Feed: 
Lbs/hour, 12,700 -- 
Temperature, .degree.F., 
480 300-500 
Pressure, psig 600 50-650 
(17) Steam Yield: 
Lbs/hour, 12,700 -- 
Temperature, .degree.F., 
488 300-500 
Pressure, psig, 600 50-650 
(20) Cooled Reactor Effluent: 
SCF/hour, 467,500 -- 
Lbs/CB/1000 SCF, 6.47 3 to 10 
Temperature, .degree.F., 
1,200 1000-1600 
Pressure, psig, 3 2-30 
(b) Apparatus Dimensions 
Conduit (15): 
Diameter, inches, 18 10-30 
Boiler Unit (14): 
Diameter, feet, 8 5-15 
Height, feet, 15 5-30 
Bed (49): 
Height, feet, 1.sup.(a) 
0.5-3 
.sup.(a) above grid (46), below tubes (9) 
Tubes (9): 
Number used, 10 3-25 
Diameter, feet, 2 1 to 3 
Height, feet, 5 3 to 20 
Height to Diameter Range, 
2:1 to 7:1 
Grid (46): 
Aperture Size, each, inches, 
1 0.5-3 
Total aperture area, square inches, 
174 -- 
Bed (50): 
Height, feet, 1.sup.(c) 
0.5-3 
.sup.(c) above tubes (9) 
Shell-tube exchanger is of carbon steel. 
Solids used can include sand, Al.sub.2 O.sub.3 coke, carbon black 
pellets, 
and the like. 
Specific on Al.sub.2 O.sub.3 
Particle size range, U.S. Standard mesh, 
16 to 45 10-60 
Composition: wt. % 
SlO.sub.2 2 
Al.sub.2 O.sub.3 95.5 
TiO.sub.2 2.5 
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