Rotary screen apparatus for use with cooling towers

An improved rotary screen for high volume water screening includes a rectangular truss having a forward bearing surface supporting a rotary screen element supported by a central rotating hub and a plurality of radial beams connecting to a peripheral beam. A curved support on the truss forward surface transfers screen load during use between the peripheral beam to the truss.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the screening of high volumes of water 
such as are generated in cooling towers in industrial and chemical plants. 
Even more particularly, the present invention relates to an improved 
rotary screen apparatus wherein a structural deep frame carries a rotary 
screen element on its forward surface and wherein load is transferred from 
the screen to the frame via a central hub of the screen and a peripheral 
beam support on the frame, and wherein radial struts of the screen 
extending between the hub and its periphery support the frame against the 
load transfer thereto by high flow of water across the screen. 
2. General Background 
In petrochemical plants and other such refineries, and in some industrial 
applications, large cooling towers are used to provide heat transfer for 
various processes. Typically, in the petrochemical industry very large 
cooling towers can generate an enormous volume of water which must be 
continuously recirculated, screened, and treated. Most bar screens are 
highly complicated devices using travelling belts that must be supported 
at the ends of the belt by tensioning mechanisms that are complicated, 
expensive, and often require extensive maintenance. Several devices have 
been patented which relate to screened devices which move or rotate in 
order to continuously remove filtered material from the flow stream. The 
following table lists various patents that include water intake screens 
and screening devices for use in treating water and waste streams. 
______________________________________ 
Patent No. 
Title Issue Date 
______________________________________ 
4,582,601 
Polymeric Basket Frame For A 
04/15/86 
Traveling Water Screen 
4,541,930 
Interchangeable Screen Panels 
09/17/85 
For A Traveling Water Screen 
4,343,698 
Water Intake 08/10/82 
4,198,299 
Microscreen Method And Apparatus 
04/15/80 
4,192,749 
Screens For Water Intakes 
03/11/80 
3,893,923 
Screening And Comminuting Device 
07/08/75 
3,351,204 
Filtering Device 11/07/67 
2,022,336 
Self Cleaning Screen 11/26/35 
2,013,971 
Automatic Screening And 
09/10/35 
Filtering Apparatus 
1,740,578 
Screen 12/24/29 
1,516,693 
Rotary Strainer 11/25/24 
______________________________________ 
SUMMARY OF THE INVENTION 
The present invention provides an improved rotary screen filter apparatus 
for use in high quantity filtration of cooling tower water. The apparatus 
includes a structural truss frame having first and second spaced-apart, 
generally rectangular frame members defining front and rear surfaces and a 
plurality of fore/aft extending beam struts joining the front and rear 
frame members, forming a truss therewith. A rotary shaft is mounted to the 
truss and extends fore/aft in the central portion of the truss generally 
between the front and rear surfaces thereof. 
A rotary screen is mounted on the shaft for rotation with respect to the 
truss, the screen comprising a central hub, a plurality of radially 
extending, circumferentially spaced beams extending from the hub and 
mounted rigidly thereto, and a peripheral circular beam defining the 
periphery of the screen at the end of each radial beam, the radial beam 
being rigidly attached to the peripheral beam, and a layer of screen 
attached to and supported by the combination of the hub, radial beams and 
peripheral beams. 
A peripheral curved track mounted on the upstream surface of the truss is 
shaped to track of the periphery of the screen through at least an obtuse 
angel of about 180.degree., the track including a backing member that 
supports the periphery of the screen at the peripheral beam on the 
downstream side of the screen. 
The present invention relates to an improved rotary screen filter useful in 
the safe and efficient operation of industrial cooling water system 
equipment. The present invention provides a method of prevention of damage 
and subsequent unanticipated shutdown of cooling water system pumps as 
incurred by floating debris from the attached and adjacent cooling tower 
water basin. Uninterrupted free flow of pumped cooling water designed to 
service industrial equipment operations where petrochemical distillation, 
electrical generation, and refrigeration is the ultimate goal, and is of 
utmost importance for maintaining safe operating parameters necessary to 
control equipment performance. Uncontrolled operating parameters such as 
that caused by the loss of cooling water can and do affect hydrocarbon and 
other hazardous materials within the pressure containing vessels to the 
point of danger and catastrophe. Hence, proper operation of primary and 
secondary cooling water pumps cannot be ignored, due to the hazards which 
can subsequently be presented to plant and public persons and property in 
the vicinity of aforementioned primary operating equipment. 
The present invention is superior to prior art designs installed for the 
purpose of screening and preventing debris which may cause intermittent 
shutdown of cooling water pumps. 
The key design factor in successful long term operation of this apparatus 
and related hazardous industrial equipment is the convenience of cleaning 
and removing debris without safety hazards, expense, and hardships imposed 
by currently used designs. The circular rotating screen section of this 
proposed apparatus is designed of a size that is several times greater 
than the diameter of the adjacent cooling water pump suction inlet pipe or 
casing. The apparatus can be mounted to the cooling water basin walls 
prior to cooling water pumps in such a manner that all water introduced to 
the pumps'suction must pass through the center rotating screen and its 
radial bracing sections where screen material of 1/2" to 1" or larger pore 
size and 10 gauge or larger thickness, for example, provides a stop to 
larger more harmful free floating debris. 
The device consists includes a stationary supporting framework, a 
stationary debris stop screen, a rotating screen framework, a rotating 
debris stop screen, a rotating hub and shaft, and rotating debris stop 
shaft bearings. 
The stationary framework can be rectangular in shape and sized to fit an 
individual pump sump entrance flue configuration. The support framework is 
constructed of beams of galvanized carbon steel or stainless steel 
material to meet customer requirements for corrosion protection. The front 
surface of the frame has a half circular shape which locks in with the 
rotating debris stop screen for preventing passage of free floating 
materials to the pump suction. 
The stationary debris stop screen material is made of carbon steel 
galvanized or stainless steel 10-gauge or better screen or expanded metal. 
The screen material is attached to the stationary debris stop framework by 
welding with compatible metal filler materials or attached by 
bolts/nuts/clamp devices of same construction metals. 
The rotating debris stop screen framework is made of carbon steel, 
galvanized, or stainless steel 1/4" angle-iron rolled to a circle and 
welded in one place with compatible materials to make a complete circular 
frame. Radial braces are attached to the interior of the circular frame at 
a hub and then attach to the metal donut piece to which the shaft is 
attached. Size of this component depends upon that required to adequately 
give coverage to the opening of the sump inlet to the pump suction. 
The rotating debris stop screen can be constructed, for example, of carbon 
steel galvanized or stainless steel 10-gauge or better screen material or 
expanded metal. The screen material is attached to the rotating circular 
debris stop framework and radial bracing pieces by welding with compatible 
metal filler materials or attached by bolts/nuts/clamp devices of same 
construction materials as the framework to prevent galvanic corrosion. 
Size of the rotating debris stop screen is the same as that of the 
rotating debris stop frame which is dependent upon the opening of the sump 
inlet to the pump suction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 illustrate the preferred embodiment of the apparatus of the 
present invention designated generally by the numeral 10. Rotary screen 
apparatus 10 has particular utility in the screening of very high volumes 
of water, such as is typically incurred in the operation of petrochemical 
and refinery cooling towers. These cooling towers can be, for example, 
several stories high and generate enormous volumes of water on a 
continuously circulating basis. In FIG. 1, an exit flume 12 is shown which 
carries effluent water from a cooling tower in a channel fashion to a 
pump. Flume 12 is defined by a bottom wall 13 which is substantially flat, 
and a pair of generally vertical sidewalls 14 producing a generally square 
or rectangular cross-sectional flow zone. Flume 12 can be constructed of 
reinforced concrete, for example. The flume includes an influent end 
portion 16 that communicates directly with the cooling tower (not shown), 
and an exit flume 17 that carries effluent away from the screen 10 
apparatus to a pump for recirculation or discharge. Arrows 18 in FIG. 1 
indicate the direction of flow of fluid between influent 16 and effluent 
17 end portions of flume 12. 
In FIGS. 2-4, there can be seen more particularly the construction of 
screen apparatus 10. An enlarged generally rectangular frame 20 is 
provided which includes bottom wall 21 and a pair of generally vertically 
upstanding sidewalls 22, 23. Each of the walls 21, 23 is bordered by a 
plurality of structural peripheral beams so that each wall is rigid, 
preferably manufactured of welded steel flanged beam construction. Screen 
material can be used to cover each wall 21-23, such as, for example, 
expanded metal. A top wall 24 likewise is comprised of a plurality of 
structural steel flanged beams, such as angle shapes for example. 
Top wall 24 carries a plurality of downwardly depending struts 25 that 
supports plate 28 and one or more bearings 26 for supporting rotary shaft 
27. Shaft 27 forms a connection with hub 41 of rotary screen element 40. 
Frame 20 provides a forward surface 30 which is substantially flat covered 
with forward screen element 31 and a rear surface 32 which is 
substantially flat but which is not screened. The frame 30 extends 
vertically and laterally as well as longitudinally so that the frame has a 
thickness of approximately one foot (1') as compared to a rotary screen 40 
diameter of approximately eight feet - ten feet (8'-10'). Thus, the frame 
20 provides a rigid truss for carrying the load that is transferred from 
the travelling stream of fluid contained in flume 12 to the rotary screen 
element 40. The load from rotary screen element 40 is transferred to frame 
20 at shaft 27, and at peripheral curved track 33 which acts as a beam 
support. Curved track 33 is of a generally U-shape configuration, 
extending approximately 180.degree. about the rotary screen element 40, as 
shown in FIGS. 1 and 2. The peripheral beam 33 is L-shaped in cross 
section, including a backing flange member 34 and a peripheral flange 
member 35. The peripheral flange member 35 tracks the contour of the 
periphery 42 of screen element 40 which is circular in configuration. 
A plurality of paired beams extend radially from hub 41 to the periphery 42 
of screen element 40. Each pair of beams includes a beam 43 on the 
upstream surface of screen element 45 and a downstream beam 44 on the 
downstream side of screen element 44. Thus, the screen 45 is sandwiched 
between forward, upstream radial beams 43 and correspondingly positioned 
downstream beam elements 44. Additionally, the periphery 42 of element 40 
includes upstream 46 and downstream 47 beams placed on opposites sides of 
screen element 45, as shown in FIGS. 5 and 6. Thus, substantially all of 
the load generated by the flowing stream of fluid in flume 12 is carried 
by flanged beams including the plurality of upstream and downstream radial 
beams 43, 44 which span between hub 41 and periphery 42 which includes 
peripheral beams 46 and 47. Load is transferred from the hub to shaft 27 
and then to struts 25 and to support plate 28. At the periphery, the 
plurality of beams 43, 44 form a structural connection with the 
peripheral, generally circular beams 46, 47, and transfer load from those 
beams to the generally U-shaped beam 33. The flange 35 insures proper 
alignment of screen 40 while the beam element 34 and the element 35 carry 
any load which tends to deflect the screen 40 rearwardly. Since frame 20 
is of a truss-like configuration which includes not only forward 30 and 
rear 32 surfaces which are spaced apart but also sidewalls 21-23 for added 
support. This frame 20 carries a full load which is transmitted thereto 
via the shaft 2 and the peripheral beam 33. 
Sprayers 50 can be positioned on the top of frame 20 for backflushing 
screen 45, as shown in FIG. 4, the spray of water being indicated by the 
numeral 51. 
Trough 52 extends transversely across the forward face of screen 40 for 
catching debris that drops off the forward face of screen element 45 
during backwashing with sprayers 50. A pair of forwardly extending 
supports 53, 54 support trough 52 in position. 
Because many varying and different embodiments may be made within the scope 
of the inventive concept herein taught, and because many modifications may 
be made in the embodiments herein detailed in accordance with the 
descriptive requirement of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not in a limiting 
sense.