Integral flow circulator for fluid bed reactor

A fluid bed reactor includes an integral flow circulator which eliminates the need for recirculation equipment external to the reactor and permits utilization of multiple distributor modules to provide a wide range of reactor capacities.

BACKGROUND OF THE INVENTION 
This invention is directed to an integral internal circulation system for a 
fluid bed biological or adsorption reactor. 
Fluid bed reactors have been demonstrated as effective supplemental or 
replacement reactors for adsorptive or biological treatment of waste water 
for BOD removal, nitrification and denitrification. Fluid bed reactors, as 
stated, may be biological or adsorptive in character. In biological 
reactors, the treatment is accomplished primarily by microorganisms which 
feed on the nutrients in the wastewater. In adsorptive reactors the 
treatment is primarily physical with the impurities in the wastewater 
being adsorbed and so entrapped on an appropriate medium such as activated 
carbon. 
The basic apparatus and methods of operation of fluid bed biological 
reactors are disclosed and covered in a series of patents including U.S. 
Pat. No. 3,846,289, issued Nov. 5, 1974, U.S. Pat. No. 3,956,129, issued 
May 11, 1976, U.S. Pat. No. 4,009,099, issued Feb. 22, 1977 and U.S. Pat. 
No. 4,009,098, issued Feb. 22, 1977. 
These patents disclose that, in a fluidized bed environment, where solid 
particles, such as sand, form a bed which is suspended in an upwardly 
flowing liquid stream with the particles in continuous motion, an enormous 
surface area for biological growth is available. When appropriate 
conditions of temperature, pH, availability of food, absence or presence 
of oxygen, are maintained, biological growth is remarkably rapid so that 
the reactor volume required and the retention time necessary to achieve a 
given biological conversion are drastically reduced. Accordingly, then, 
substitution of fluid bed biological reactors for the reactors in common 
use today, gives promise that the land area now devoted to biological 
treatment plants, can, in the future, be significantly reduced. 
In another patent, U.S. Pat. No. 4,202,774, issued May 13, 1980, it is 
pointed out that while fluidization and suspension of particulate solids 
are extremely important in promoting biological growth on the solids in 
fluid bed biological processes, excessive agitation of the solids is to be 
avoided to reduce abrasion of the solids with resultant removal of the 
biological growth. In order to avoid the deleterious effects of excessive 
agitation of the fluidized particulate solids, the patent discloses novel 
liquid flow distributors capable of introducing influent into the fluid 
bed reactor and directing large flow volumes vertically upward in the 
reactor without causing excessive turbulence therein. 
In fluid bed waste water reactors of the type described above, a certain 
loading rate (mass loading) on the reactor is required to allow the 
desired biological reactions to occur, and this sets a limit on the volume 
of untreated waste water which can be introduced into a reactor of given 
size in a specified period of time. However, for this same reactor, there 
is a minimum flow of liquid into the reactor which must be observed to 
maintain the necessary degree of fluidization of the particulate solids. 
In order to satisfy both conditions, recirculation of the liquid from 
above the fluidized bed to the reactor liquid flow distributor is 
undertaken; the necessary flow rate for fluidization is thus achieved, 
while the influent can be limited to that flow which can be adequately 
treated in the reactor. 
The recirculation circuit which has been used is a system external to the 
reactor and includes a pump, a conduit connecting the region of the 
reactor above the fluidized zone of the reactor with the pump for 
withdrawing liquid from that region and a conduit connecting the pump to a 
region below the fluidized zone of the reactor for reinjection of the 
liquid to maintain fluidization. The piping for such installations, with 
pipes often having a diameter of 24 inches or more, is expensive; the cost 
of external recirculation piping for a typical reactor representing 15 to 
20% of the installed cost. 
Accordingly, a very real need exists for an improved recirculation system 
for fluid bed reactors. 
In the main, prior art structures, if at all relevant, are generally 
directed to sand filters rather than fluid bed reactors. In the process of 
sand filtration, the liquid to be filtered passes downwardly through a 
sand bed which removes particulate material from suspension in the liquid. 
This downflow system does not result in fluidization of the sand particles 
during normal operation. The following patents show various aspects of the 
prior art in sand filters: 
______________________________________ 
U.S. Pat. Nos. 
______________________________________ 
1,138,634 J. M. Davidson 
May 1915 
1,919,565 W. C. Laughlin 
July 1933 
2,199,891 M. J. Martin May 1940 
3,512,649 R. Nebolsine et al 
May 1970 
3,625,365 J. E. Armstrong 
December 1971 
______________________________________ 
The following U.S. patent is directed to a reaction vessel for a catalytic 
gas-liquid reaction in which recycle of liquid, which separates from vapor 
in an upper chamber of the reactor, is provided: 
______________________________________ 
U.S. Pat. No. 3,414,386 
E. D. Mattix 
December 1968 
______________________________________ 
SUMMARY OF THE INVENTION 
In accordance with this invention, the recirculation system for the fluid 
bed reactor is almost completely within the reactor tank; no external 
piping is required for recirculation. 
More particularly, a reactor tank is provided with a circulator therein 
comprising a column conduit extending from the bottom to the top of said 
reactor tank and having a pump therein for directing a downward flow of 
liquid through said column conduit, one or more fixed, perforated, 
horizontal collection manifolds in flow connection with said column 
conduit and positioned at a level in said reactor tank below the surface 
of the liquid in said tank but above the level of fluidized particulate 
solids therein, one or more fixed, horizontal, distributor headers 
adjacent the bottom of said reactor tank in flow communication with said 
column conduit, distributor pipes connected to said distributor headers to 
provide generally uniform discharge of liquid over the cross-section of 
the reactor tank and an influent pipe in flow connection with said column 
conduit. 
The reaction tank is provided with a cover when anaerobic processes are 
contemplated to trap gases, particularly methane, produced in such 
processes. In such an anaerobic reaction tank, it is preferred to provide 
an enclosed pump well surrounding the conduit column in the upper portion 
thereof, so that only the gas in the pump well is discharged into the 
atmosphere when pump maintenance is required. A gas conduit is provided to 
draw off the gas from the gas space under the reactor cover outside the 
pump well. 
The reactor tanks of the invention lend themselves to modular development 
when reactor tanks of rectangular cross-section are employed. In such 
cases, a flow distributor module can be constructed in a rectangular 
configuration with each distributor header having a plurality of 
distribution pipes of uniform length fixed in perpendicular relationship 
to each distributor header in a horizontal plane. A plurality of flow 
distributor modules can be employed in a rectangular reactor tank served 
by a single column conduit. 
These and other features and advantages of the invention will become more 
clear from the following description of the preferred embodiment and the 
drawings.

DETAILED DESCRIPTION 
While the structures of the invention may be used to carry out processes of 
either the biological or adsorptive type, the description below refers 
primarily to reactors intended to carry out biological reactions. 
In FIG. 1, one embodiment of the fluid bed biological reactor 10 with 
integral internal circulator 40 is shown which includes the reactor tank 
20 having sidewall 21, airtight cover 22 and tank bottom 24. The reactor 
tank 20 may have either a circular or rectangular cross-section. Within 
the reactor tank 20, the circulator structure 40 is provided having, at 
its main components, a column conduit 42 which extends from the tank cover 
22 to the tank bottom 24, inlet manifolds 60 in flow connection with the 
upper end of said column conduit 42, and a flow distributor 80 in flow 
connection with the lower end of column conduit 42. In the covered reactor 
tank 29 there is a body of wastewater 12 undergoing biological reaction 
having an upper surface 14 above which there is a gas space 25 which 
extends between the upper surface 14 and the cover 22. Within the body of 
wastewater 12 there is a zone of fluidized particulate solids which 
extends upward from the flow distributor 80 to the level 18, the precise 
position of which level varies with the upward velocity of the incoming 
fluid, the density of the particulate solids having biological growth 
thereon and the frequency of biological growth removal. Above level 18 in 
the reactor tank 20 there is a freeboard zone 19 which is essentially 
devoid of particulate solids. A wastewater inlet 26 is provided into 
reactor tank 20, a methane gas outlet pipe 28 opens into gas space 25 
while an effluent off-take 32 having a vent 33 is in flow connection with 
zone 19 within reactor tank 20. 
The column conduit 42 consists of a lower section 41, which is essentially 
a straight vertical conduit connected at its lower extremity to the flow 
distributor 80, and an upper section 44 in which there is a pumping 
element 46. Drive shaft 54 passes axially through conduit section 44 to 
connect pump 46 to the pump motor 50. Pump motor 50 is mounted on motor 
support 52 which, in turn, is mounted on access cover 34. The access cover 
34 is bolted to tank cover 22 of reactor tank 20. The upper section 44 of 
column conduit 42 is in flow communication with the collection manifold 
60. 
Surrounding the upper section 44 of column conduit 42 is a pump well 50 
having an upper cylindrical wall section 51 which is sealingly joined to 
the tank cover member 22 by weldments 56. A transition wall member 52 of 
generally conical configuration joins the cylindrical upper portion 51 to 
the lower column conduit section 41. The upper section 44 of column 
conduit 42 is open to the pump well 50 through ports 48. The pump outlet 
65 which is situated at the lower end of the upper section 44 of column 
conduit 42 is slidably seated in a cylindrical centering sleeve 67 which 
is centrally fixed relative to the lower section 41 of column conduit 42. 
The slidable contact is afforded by o-rings 69, fixed in grooves 71 
provided on the outer surface of pump outlet 65, which engage centering 
sleeve 67. 
Collection manifolds 60 extend across reactor tank 20 in freeboard region 
19 from points adjacent the reactor tank wall 21 to join with pump well 50 
at ports 61 in the wall member 51 or 52 of the pump well 50. 
The collection manifolds 60 have a plurality of collection ports 64 along 
the upper surface of the manifolds. Manifolds 60 are located in the 
freeboard region 19 within the reactor tank 20. 
Adjacent the bottom of the reactor tank 20 is the flow distributor 80 in 
which a plurality of distributor headers 82 are connected to the column 
conduit 42. Each of the distributor headers 82 has an array of distributor 
pipes connected thereto. The distributor pipes 84 have a plurality of 
ports (not shown) along the bottom thereof in flow connection with the 
flow skirts 86 which provide a channel toward the narrow bottom end of the 
troughs 88 formed by the crenolated bottom 24 of the reactor tank 20. Hold 
down bars 92 which are anchored by pins 94 to the concrete foundation 
underlying the reactor tank 20 may be provided to prevent the tendency of 
the arrays of distributor pipes 84 to rise in the reactor tank. 
In operation wastewater is admitted through waste water inlet 26 into the 
pump well 50 and flows to the ports 48 of the upper section 44 of column 
conduit 42. In addition, recirculating wastewater flowing through 
collection ports 64 of the collection manifolds 60 enters the pump well 50 
through ports 61 and joins the wastewater admitted through inlet 26 in 
flowing through ports 48. The wastewater admitted into section 44 of 
column conduit 42 flows vertically downward in conduit 44 under the 
influence of pump 46 which forces the wastewater vertically downward 
through pump outlet 65 into the lower section 41 of column conduit 42. The 
wastewater passes from column conduit 42 to distribution headers 82 to 
flow distributor 80 and from the headers 82 to the distributor pipes 84. 
From the distributor pipes 84 the flow passes downwardly into flow skirts 
86 and emerges and turns upwardly in troughs 88 to fluidize the 
particulate solids in the fluidized bed 16. The liquid flow continues 
upwardly into the relatively clear freeboard zone 19 and then passes the 
collection manifolds 60 with a large portion of the liquid flow passing 
into collection ports 64, while the remainder passes into the vented 
outlet pipe 32 through which it is routed for further treatment or 
disposal. The gases produced in the reaction occurring in the reaction 
tank 20 collect in the gas space 25 above the liquid level 14 and pass 
finally through gas outlet 28. Since a large proportion of the gas 
produced is methane, the gas may be burned for heating purposes or for 
power generation. 
It will be appreciated that the upper section 44 of the column conduit 42, 
with the pump 46 therein, is readily removable from the reactor tank 20 
for repair or replacement. All that is required for removing section 44 is 
purging of the gas space 27 and unbolting the cover element 34 and sliding 
section 44 out of the pump well 50. It should be noted that the only gas 
which escapes during this operation is that in the gas space 27 in the 
pump well 50 and that the gas in gas space 25 is in an entirely sealed 
region. 
The alternate embodiment shown in FIG. 2 is directed to a structure in 
which escaping gas is not a serious problem and, therefore, a pump well is 
not required. In this embodiment, the collection manifolds 60 are joined 
directly to the upper section 44 of the column conduit 42. 
It will be appreciated that when the reactor tank 20 has a cylindrical 
configuration and, hence, a circular cross section, the distributor pipes 
84 associated with each distribution header 82 are all of different 
lengths. Thus, a distribution pipe near column conduit 42 may have a 
length approaching the diameter of the cylindrical tank, but each pipe 
further away from the column conduit 42 will be slightly shorter in length 
than its neighbor, since the pipes are arranged on chords of the circular 
cross-section of the cylindrical tank and the chords diminish in length as 
distance from the center of the circle increases. The distribution pipe at 
the outer extremity of the distribution header 82 will be the shortest 
distribution pipe. 
A rectangular array of distribution pipes is an arrangement in which all of 
the distribution pipes may be of equal lengths. Such rectangular arrays of 
distribution pipe permit modular development, with a plurality of such 
rectangular arrays used for achieving economy of scale. In FIGS. 3 and 4 
such a modular development is shown in which a rectangular reactor tank 20 
is provided. Within the tank 20 is positioned a column conduit 42 of 
structure exactly similar to that described above, but extending slightly 
below tank bottom 24. Also in tank 20 are a pair of flow distributors 95 
of rectangular configuration. Each of the flow distributors 95 includes a 
distributor header 96 and a plurality of pipe distributors 98 of uniform 
length arranged along the length of the distributor header 96 and 
perpendicular thereto to give the rectangular configuration of the flow 
distributors 95. A pair of feeder conduits 90 are provided in trenches 
beneath the tank bottom 24 and are connected at one end to column conduit 
42. At the outer end of each feeder conduit 90 is a 90.degree. elbow 92 
oriented to open vertically upward. The elbow 92 joins a tee 93 in the 
distributor header 96. 
While a top feed for the incoming wastewater has been illustrated, it will 
be understood that the wastewater inlet pipe could be arranged to pass 
through the side of tank 20 for connection with the lower section 41 of 
column conduit 42. 
There has thus been disclosed a novel internal circulation system for a 
fluid bed reactor which eliminates expensive external piping and lends 
itself to modular development. 
It is expressly understood that the present invention is not limited to the 
embodiment illustrated and described. Various changes can be made in the 
design and arrangement of parts without departing from the spirit and 
scope of the invention as the same will now be understood by those skilled 
in art.