Integrated Fan Drive System For Cooling Tower

Abstract

A drive system for driving a fan in a wet cooling tower, wherein the fan has a fan hub and fan blades attached to the fan hub. The drive system has a high-torque, low speed permanent magnet motor having a motor casing, a stator and a rotatable shaft, wherein the rotatable shaft is configured for connection to the fan hub. The drive system includes a variable frequency drive device to generate electrical signals that effect rotation of the rotatable shaft of the motor in order to rotate the fan.

Claims

1. A direct drive system configured to drive a fan in a cooling tower, comprising: a variable speed permanent magnet motor comprising a rotatable shaft configured to be directly attached to a fan in a cooling tower; and a variable frequency drive device to control the speed, direction and torque of the motor, the variable frequency drive device being configured to receive control signals that represent a desired motor rotational speed and direction, and in response, generate electrical signals for input into the motor to cause the motor to operate at a motor rotational speed and direction that are substantially the same as the desired motor rotational speed and direction, respectively.

2. The direct drive system according to claim 1 wherein the variable frequency drive device includes a control signal input port to allow the variable frequency drive device to be monitored and controlled by an external computer.

3. The direct drive system according to claim 1 further comprising a vibration sensor to sense vibrations and output signals representing the sensed vibrations.

4. A cooling tower, comprising: a cooling tower structure; a variable speed permanent magnet motor supported by the cooling tower structure and comprising a rotatable shaft configured to be directly attached to a fan in a cooling tower; a cooling tower fan directly attached to the rotatable shaft of the motor such that the fan rotates with the rotatable shaft; and a variable frequency drive device to control the speed, direction and torque of the motor, the variable frequency drive device being configured to receive control signals that represent a desired motor rotational speed and direction, and in response, generate electrical signals for input into the motor to cause the motor to operate at a motor rotational speed and direction that are substantially the same as the desired motor rotational speed and direction, respectively.

5. The cooling tower according to claim 4 further comprising a vibration sensor to sense vibrations and output signals representing the sensed vibrations.

6. The cooling tower according to claim 4 further wherein the variable speed permanent magnet motor is positioned such that the rotatable shaft is oriented in a substantially vertical position.

7. A direct drive system configured to drive a fan in a cooling tower, comprising: a variable speed permanent magnet motor comprising a rotatable shaft configured to be directly attached to a fan in a cooling tower, the motor including a vibration sensor to sense vibrations and output signals that represent the sensed vibrations; and a motor control device to provide electrical signals to the control the speed, direction and torque of the motor.

8. The direct drive system according to claim 7 wherein the motor control device is programmable.

9. The direct drive system according to claim 7 wherein the motor control device comprises a variable frequency drive device.

10. A direct drive system configured to drive a fan in a cooling tower, comprising: a variable speed permanent magnet motor comprising a rotatable shaft configured to be directly attached to a fan in a cooling tower, the motor including means to sense vibrations and output signals that represent the sensed vibrations; and means to provide electrical signals to the control the speed, direction and torque of the motor.

11. A cooling tower, comprising: a cooling tower structure; a variable RPM electric motor supported by the cooling tower structure and including a rotatable shaft; a motor control device to control the RPM, direction and torque of the motor; a cooling tower fan system comprising a fan directly attached to the rotatable shaft of the motor such that the fan rotates with the rotatable shaft; and at least one vibration sensor to sense vibrations and output signals representing sensed vibrations.

12. The cooling tower according to claim 11 wherein the motor is a permanent magnet motor.

13. The cooling tower according to claim 11 wherein the motor control device comprises a variable frequency drive device.

14. The cooling tower according to claim 13 wherein the variable frequency drive device includes a control signal input port for receiving control signals from an external computer.

15. The cooling tower according to claim 13 wherein the variable frequency drive device is programmable and comprises a microprocessor, a user interface in data signal communication with the microprocessor and a device to indicate motor status.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figures, submitted for the purposes of illustration only and not intended to define the scope of the invention, in which:

[0017] FIG. 1 is an elevational view, partially in cross-section, of a fan cylinder supported by a fan deck of a cooling tower, a fan within the fan cylinder and a prior art gearbox-type fan drive system;

[0018] FIG. 2A is an elevational view, partially in cross-section, of a fan cylinder supported by a fan deck of a cooling tower, a fan within the fan cylinder and the fan drive system of the present invention;

[0019] FIG. 2B is a plot of motor speed versus horsepower for a high torque, low speed permanent magnet motor used in one embodiment of the fan drive system of the present invention;

[0020] FIG. 3 is a block diagram of the fan drive system of the present invention;

[0021] FIG. 4 is a graph illustrating a comparison in performance between the fan drive system of the present invention and a prior art gearbox-type fan drive system that uses a variable speed induction motor; and

[0022] FIG. 5 is a schematic diagram showing the fan drive system of the present invention in conjunction with a plurality of performance monitoring sensors.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] Referring to FIG. 1, there is shown a prior art mechanical fan drive system, and a portion of a wet cooling tower. The remaining portion of the wet cooling tower is not shown since the structure and operation of wet cooling towers is well known in the art. Fan cylinder 10 is positioned on fan deck 12 of the cooling tower. The prior art mechanical fan drive system comprises induction motor 14, drive shaft 16, couplings 18 and 20, and right-angle gearbox 22. Motor 14 is seated on and/or secured to fan deck 12. Gearbox or gear reducer 22 is mounted to or supported by fan deck 12. Gearbox 22 has a vertical shaft 24 that rotates upon rotation of drive shaft 16. As shown in FIG. 1, fan 27 is located within fan cylinder 10 and comprises hub 28 and fan blades 30 that are attached to hub 28. Vertical shaft 24 is connected to fan hub 28. Thus, rotation of vertical shaft 24 causes rotation of fan hub 28 and fan blades 30.

[0024] Referring to FIG. 2A, there is shown the fan drive system of the present invention. Similar to the view of FIG. 1, a portion of the cooling tower is only shown in FIG. 2A. The fan drive system of the present invention comprises variable frequency drive (VFD) device 50 and motor 52. In accordance with the invention, motor 52 is a high torque, low speed permanent magnet motor. Permanent magnet motor 52 has a high flux density. The superior results, advantages and benefits resulting from permanent magnet motor 52 are discussed in the ensuing description. VFD device 50 and permanent magnet motor 52 are mounted to or supported by fan deck 12. VFD device 50 is in electrical signal communication with permanent magnet motor 52 via cables or wires 54. Permanent magnet motor 52 has shaft 56 that rotates when the appropriate electrical signals are applied to permanent magnet motor 52. Shaft 56 is connected to fan hub 28. Thus, rotation of vertical shaft 56 causes rotation of fan hub 28 and fan blades 30.

[0025] Referring to FIGS. 2A and 3, VFD device 50 comprises a variable frequency controller 60 and a user or operator interface 62. VFD device 50 controls the speed, direction (i.e. clockwise or counterclockwise), and torque of permanent magnet motor 52. AC input power is inputted into variable frequency controller 60 via input 64. Variable frequency controller 60 converts the AC input power to DC intermediate power. Variable frequency controller 60 then converts the DC power into quasi-sinusoidal AC power that is applied to permanent magnet motor 52. User interface 62 provides a means for an operator to start and stop permanent magnet motor 52 and adjust the operating speed of motor 52. In a preferred embodiment, user interface 62 comprises a microprocessor, and an alphanumeric display and/or indication lights and meters to provide information about the operation of motor 52. User interface 62 further includes a keypad and keypad display that allows the user to input desired motor operating speeds. VFD device 50 includes input and output terminals 70 and 72 for connecting pushbuttons, switches and other operator interface devices or controls signals. In a preferred embodiment, VFD device 50 further includes a serial data communication port 80 to allow VFD device 50 to be configured, adjusted, monitored and controlled using a computer. In one embodiment, VFD device 50 includes sensor signal inputs 82, 84, 86, 88 and 89 for receiving sensor output signals. The purpose of these sensors is discussed in the ensuing description.

[0026] Referring to FIGS. 2A and 5, permanent magnet motor 52 is directly coupled to the fan hub 28. Since permanent magnet motor 52 is controlled only by electrical signals provided by VFD device 50, there is no drive shaft, couplings, gear boxes or related components as is found in the prior art gearbox-type fan drive system shown in FIG. 1. In accordance with the invention, permanent magnet motor 52 is a high-torque, low speed motor. Permanent magnet motor 52 is of simplified design and uses only two bearings 90 and 92 (see FIG. 5). Permanent magnet motor 52 includes stator 94. Such a simplified design provides relatively high reliability as well as improved and cost-effective motor production. Permanent magnet motor 52 has relatively low maintenance with a three year lube interval. Permanent magnet motor 52 can be configured with sealed bearings. Permanent magnet motor 52 meets or exceeds the efficiency of Premium Efficiency Induction Motors. Permanent magnet motor 52 substantially reduces the man-hours associated with service and maintenance that would normally be required with a prior art, induction motor fan drive system. In some instances, permanent magnet motor 52 can eliminate up to 1000 man-hours of maintenance and service. Such reliability reduces the amount of cell outages and significantly improves product output. In one embodiment, permanent magnet motor 52 has the following operational and performance characteristics: [0027] Speed Range: 0-250 RPM [0028] Maximum Power: 133 HP/100 KW [0029] Number of Poles: 16 [0030] Motor Service Factor: 1:1 [0031] Rated Current: 62 A (rms) [0032] Peak Current: 95 A [0033] Rated Voltage: 600 V [0034] Drive Inputs: 460 V, 3 phase, 60 Hz, 95 A (rms max. continuous)
FIG. 2B shows a plot of speed vs. horsepower for high torque, low speed permanent magnet motor 52. However, it is to be understood that the aforesaid operational and performance characteristics just pertain to one embodiment of permanent magnet motor 52 and that motor 52 may be modified to provide other operational and performance characteristics that are suited to a particular application.

[0035] Referring to FIG. 4, there is shown a graph that shows Efficiency % versus Motor Speed (RPM) for the fan drive system of the present invention and a prior art fan drive system using a variable speed, induction motor. Curve 100 pertains to the present invention and curve 102 pertains to the aforementioned prior art fan drive system. As can be seen in the graph, the efficiency of the present invention is relatively higher than the prior art fan drive system for motor speeds between about 60 RPM and about 200 RPM.

[0036] Referring to FIG. 5, in a preferred embodiment, the fan drive system of the present invention further comprises a plurality of sensors 200, 202, 204, 206 and 208 that provide sensor signals to sensor signal inputs 82, 84, 86, 88 and 89, respectively, of VFD device 50. Sensors 200 and 202 are positioned in proximity to bearings 90 and 92, respectively, of permanent magnet motor 52 in order to sense vibration and heat. Sensor 204 is positioned on stator 94 of permanent magnet motor 52 to monitor heat at stator 94. Sensor 206 is positioned down stream of the air flow created by fan 27 to measure airflow. For purposes of simplifying FIG. 5, fan 27 is not shown. Sensor 208 is located within the basin (not shown) of the wet cooling tower to sense the temperature of the water within the basin. All sensor output signals applied to sensor signal inputs 82, 84, 86, 88 and 89 are inputted into user interface 62 of VFD device 50 and are then routed to an external processing device, such as computer 300, via data port 80. Computer 300 includes a display screen device 302 that enables a user or operator to visually monitor the data outputted by sensors 200, 202, 204, 206 and 208. Computer 300 further includes a user interface, e.g. keyboard, (not shown) that allows an operator to input commands. Computer 300 is configured to implement a reliability algorithm using the data outputted by sensors 200, 202, 204, 206 and 208 and in response, output appropriate control signals that are inputted into user interface 62 via data port 80. Such control signals can be used to adjust the speed of motor 52. Thus, the sensors and computer 300 provide a feedback loop that: [0037] a) monitors vibrations and heat at the bearings of motor 52; [0038] b) monitors heat at the stator of motor 52; [0039] c) monitors airflow produced by fan 27; [0040] d) monitors the temperature of the water in the cooling tower basin; [0041] e) provides a trim balance to compensate for fan-unbalance inertia on the cooling tower structure (i.e. Hula Effect); [0042] f) alerts the operators to a blade-out situation and automatically reduces the speed of motor 52; [0043] g) locks out a particular motor speed that creates resonance; [0044] h) alerts the operator to ice accumulation on fan blades 30 and automatically initiates de-icing operations; and [0045] i) routes the basin-water temperature data to other portions of the industrial process so as to provide real-time cooling feedback information that can be used to make other adjustments in the overall industrial process.

[0046] Thus, the fan drive system of the present invention provides many advantages and benefits, including: [0047] a) elimination of many components found in the prior art gearbox-type fan drives, such as drive shafts, couplings, bearings, shaft seals, etc.; [0048] b) elimination of oil changes; [0049] c) significant reduction in service and maintenance; [0050] d) ability to vary the speed of the permanent magnet motor over a relative wide range of speeds; [0051] e) ability to reverse direction of the permanent magnet motor without any additional components; [0052] f) consumption of significantly lower amounts of energy in comparison to prior art gearbox-type fan drive; [0053] g) easy retrofit with existing fan thereby eliminating need to construct new cooling towers; [0054] h) significant reduction in the occurrence of cell outages; and [0055] i) provides significantly more cooling capacity in comparison to prior art gearbox-type fan drive.

[0056] The operational logic and system architecture of the present invention will provide the ability to optimize the cooling tower for energy efficiency (e.g. at night when it is cold) and to maximize cooling on hot days or when the process demands additional cooling or to avoid fouling of auxiliary systems such as condenser and heat exchangers.

[0057] Although the foregoing discussion is in terms of the applicability of the present invention to the petroleum industry, it is to be understood that the present invention provides benefits to any industry that uses wet cooling towers. Thus, the present invention has applicability to many industries that consume large amounts of energy and are process intensive, such as the power generation, petro-chemical, pulp and paper, chemical, glass, mining, steel and aluminum industries.

[0058] It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction and/or method without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described.