Invented by Patrick M. Rollins, George M. Lucas, Prime Datum Development Co LLC
The Prime Datum Development Co LLC invention works as followsThe present invention is directed towards a load bearing direct drive system and a variable control system that can be used to efficiently manage the operation of fans within a cooling system. This could include a wet-cooling system, an air-cooled heat-exchanger (ACHE), HVAC systems, centrifugal and blowers, mechanical-towers, or chiller-systems. The load bearing direct drive system in one embodiment comprises a load-bearing torque multiplier with an output shaft that can be rotated, connected to a blower, and a motor which has a shaft that can be rotated, driving the load bearing multiplier.
Background for Direct-drive system for cooling fans, exhaust blowers, and pumps
Industrial cooling systems such as air-cooled heat-exchangers (ACHE) and wet-cooling-towers are used to remove heat from circulating cooling-water used in power plants. In the petroleum refinery industry, ACHEs and wet-cooling systems are used extensively. The cooling provided by wet-cooling heat exchangers and air-cooled towers is essential for the refining of oil. Liquid Catalytic Cracking and Isomerization are processes that refineries use to process hydrocarbons under high pressure and temperatures. The temperature and pressure of the refinery are controlled by cooling water. Loss of cooling water circulation in a refinery may lead to unsafe and unstable operating conditions, requiring the immediate shutdown of processing units. The ACHE and wet-cooling towers are now considered “mission critical assets”. For refinery production, ACHEs and wet-cooling towers have become “mission critical assets”. The reliability of cooling systems is therefore critical for refinery profit and safety. It’s affected by many factors, such as the environmental restrictions on water cooling, environmental permits, inelastic pressures from supply chains, and variable margins. Refineries have implemented many new processes to extract hydrogen from lower-value by-products, and then combine it with higher-value products. The cooling of these processes is crucial to the quality and yield of the final product. In the last decade, refineries have added processes to transform low-grade petroleum products into more profitable and higher-grade products like aviation and automobile gasoline. The wet-cooling and ACHEs are essential to these processes because they control the temperatures and pressures which affect product quality, yield and safety. These processes have also tapped into the cooling capacity reserves in the towers, leaving some refineries with a ‘cooling limit? On hot days, the cooling towers can be clogged and even blocked. ACHE cooling is different from wet cooling in that ACHEs rely on air to cool the air, as opposed latent heat of vapourization or “evaporative cooling”. The majority of U.S. refineries are operating at well over 90% capacity. This means that uninterrupted refinery operations are critical for refinery profits and to pay for the process improvements implemented in the past decade. In the March 2007 report, “Refinery Outages – Description and Potential Impact on Petroleum Product Prices”, the U.S. Department of Energy describes the effect of interruptions in cooling unit operation with regard to petroleum product prices.
A typical wet cooling system consists of a basin that holds the cooling water and is then routed through heat exchangers, condensers, etc. in an industrial facility. The cool water absorbs the heat from the hot streams of process water that must be cooled or consolidated, and this heat is used to warm the circulating water. Warm circulating water flows to the top and then trickles down over the fill material in the cooling tower. The fill material has been designed to allow maximum contact between water and air. The L/G ratio is the air-to water ratio of a wet cooling system. The water that trickles down over the fill material contacts the ambient air rising through the tower, either naturally or with the use of large fans. The cooling of water in each of the cells of a wet cooling tower is done using the above technique. The second edition of the book “Cooling Tower Fundamentals”, edited by John C. Hensley, and published by SPX Cooling Technologies, Inc., describes cooling towers in detail.
Many wet cooling towers are used today and use large fans to supply ambient air. The cooling tower’s fan deck has a fan stack that contains the fans. The fan stacks have a parabolic configuration to add fan velocity recovery and seal the fan. In some systems, the fan-stack may be shaped like a cylinder. Drive systems are used for driving and rotating the fans. The reliability of the fan-drive system is crucial to the efficiency and production of a cooling unit. In a cooling tower, the duty cycle of a fan drive system is extremely high due to extreme humidity, poor water quality, explosive gases, icing, wind shear, corrosive chemicals in water treatment, and mechanical drive requirements. Each cell in a cooling tower with multiple cells, like those used by the petroleum industry, has its own fan and fan-drive system. If the fan drive system for a cell is shut down, that cell will suffer a “cell outage”. A cell outage can result in a reduction in refined petroleum production. A ‘cell outage’, for example, can result in a decrease in refined petroleum production. Even a ‘cell outage’ lasting only one day could result in thousands of barrels of refined petroleum being lost. The percentage loss of total tower cooling potential increases as more cells go down within a certain time period. The refinery’s profitability and product output will be affected, resulting in an increase in price for the final product. Even a slight decrease in output can cause a rise in gasoline prices. The cooling BTUs are directly related to the production in barrels/day (BBL/Day).
One prior art drive system that is commonly used in wet cooling towers is an intricate, mechanical fan-drive system. The motor of this prior art fan-drive system drives the drive train. The drive train is connected to a gearbox or gear-reducer, which drives the fan blades. Referring to FIG. In FIG. The prior art fan-drive system is used in the wet cooling tower 1. Fan stack 2 and fan 3 are part of the wet cooling tower 1. Fan 3 is composed of fan hub 5A, fan blades 5, and fan seal disk 4. Fan hub 5A is connected to fan blades 5B. The prior art fan system includes a drive shaft 7 that drives a gearbox 6, which is coupled with a gearbox 6. Induction motor 8 rotates drive shaft 7 in the prior art fan driven system. The drive shaft 7 has two shaft couplings. These are not shown, but they are well-known in the industry. They are located at either end. These shaft couplings connect the draft shaft 7 with the gearbox 6 as well as the induction motor 8. The wet cooling tower 1 has a fan deck 9, on which the fan stack 2 is mounted. Gearbox 6 is supported by an induction motor 9. The ladder frame or torque tubes (not shown but well-known in the art) support both. Vibration switch are usually located on the torque tube or ladder frame. Vibration switch 8A is one such switch. 1. These vibration switches automatically shut down fans that have become unbalanced. The prior art fan drives are subject to frequent failures, have a low MTBF (Mean time between failure) and require diligent maintenance such as regular oil change in explosive and hazardous environments. The coupling and shaft aligning are crucial and require skilled craft labor. A common prior art mechanical drive is a gearbox-type fandrive with a single speed that uses five rotating shafts. It also has eight bearings, two shaft seals at high speeds, and four gears. This drive train absorbs approximately 3% of total power. While this prior art fan-drive system was initially attractively low-cost, cooling tower users found that they needed to buy heavy-duty and oversized components like composite gearbox shafts or couplings to avoid breaking the fan-drive components. This is especially true when trying to start across-the line. Some cooling tower users added additional options, such as oil bath heaters, low-oil shut-downs and anti-reverse clutches. The life cycle costs of the mechanical fan drive system prior to the invention are not comparable with the initial purchase price. Even after the user has spent more money on heavy duty components and oversize components, the reliability is still poor. This prior art gearbox drive system is low-cost initially, but has a high cost over time and poor reliability. Each cell in a multi-cell tower cooling system, like the ones commonly used by the petroleum industry, has a fan with a prior art mechanical drive system. If the mechanical fan system for a cell is shut down, that cell will suffer a “cell outage”. This was explained in the previous description. The productivity loss over time caused by the low reliability of mechanical fan drives in the prior art can be measured in terms of a percentage loss of refinery production. Data and analysis have shown that in one cooling tower system currently in operation, the loss or failure of a single cell is equivalent to a loss of 2,000 barrels of oil per day.
Other types of fan drive systems such as V belt drive systems also have many problems in terms of maintenance, MTBF, and performance, and they do not eliminate or overcome the problems associated with prior art gearbox type fan drive system. Prior art hydraulically-driven fan systems were one attempt to eliminate problems associated with prior art gearbox type fan drive systems. U.S. Pat. describes such a system. No. No.
Air Cooled Heat Exchangers are widely used in industries such as power plants, refineries, petrochemical plants, chemical plants, gas processing plants and other industrial facilities. ACHE exchangers can be used in situations where water is not available or permits are not possible. ACHEs do not have the cooling power of ‘Wet Towers’ When comparing size (also known as footprint), ACHEs lack the cooling effectiveness of?Wet Towers? footprint). ACHEs are usually made with a bundle of finned tubes. One or more large fans provide cooling air. The air is usually blown upwards by a horizontal tube bundle. Air can be pushed through the tubes or pulled by the fans. Fan-tip speeds are typically limited to 12,000 feet per minutes for aeromechanical purposes, and can be reduced in order to reduce noise. A fan stack is used to enclose the space between the fans and the tube bundle. The fan stack directs air flow over the tube assembly, thereby cooling it. The entire assembly is mounted either on legs or pipe racks. The electric motor is used to drive the fans. The fan assembly is supported on a mechanical steel drive support system. Typically, vibration switches are located on the structure supporting the fan assembly. These switches are used to shut off a fan if it becomes unbalanced. The airflow is crucial in ACHE cooling. It ensures that the air has a proper “flow field” Airflow is very important in ACHE cooling to ensure that the air has the proper?flow field? Turbulence from the current fan gear structure can reduce cooling efficiency. Mass airflow is therefore the most important parameter in removing heat from tube and bundle systems. ACHE cooling differs to wet cooling towers because ACHE cooling is “Convection cooling” As opposed to the latent energy of vaporization, or “evaporative cooling?
Previous art ACHE fan drives use a wide range of fan drive components. Electric motors, gasoline or gas engines, and hydraulic motors are examples of these components. Electric motors are the most common type of drive system. When electric power is unavailable, steam and gas are used as drive systems. With limited success, hydraulic motors were also used. Hydraulic motors are relatively inefficient, even though they provide variable speeds. Hydraulic motors can also leak, contaminating the cooling water. This requires environmental remediation. Occasionally, motor and fan speeds are controlled by variable frequency drives. This has mixed results. Most commonly, the positive-type belt drive with high torque is used. It uses sprockets which mesh with the cogs of the timing belt. These belt drives are suitable for motors with up to 60 horsepower and fans with up to 18 feet diameter. In small and medium fans, banded V belts are often used. Gear drives are used for large motors and larger fan diameters. The fan speed can be set using the right combination of timing belts, V-belts and sheaves. Gears are also used to select the proper reduction ratio. Right-angle gearboxes are often used in fan drive systems to reduce the speed and increase torque of an electrical motor offset. Belt drives, pulleys, and right-angle motor gear boxes are not reliable. To achieve reliability, the complex mechanical drive systems of prior art require strict maintenance practices. Belt tension is a major problem in ACHE fan systems. This leads to a poor belt reliability. It is common to upgrade to “timing belts”. Add a tension system. Rahadian Bayu, of PT Chevron Pacific Indonesia in Riau, Indonesia presented a technical paper entitled ‘Application Of Reliability Tool To Improve V-Belt Live On Fin Fan Cooler units? at the 2007 International Applied Reliability Symposium. It addressed the reliability and efficiency V-belts that were used to drive many fan systems prior to this. ACHE fan drives are prone to failures due to the reliability of their belt and pulley system and gear reducer. This can be detrimental for industries that depend on cooling, such as power generation, petroleum refining, and petrochemical. The motor systems in ACHE fan drives are also complex, with multiple bearings and complex valves for operation and control, as well as reciprocating parts. They must be changed at regular intervals. The production output of many industrial facilities such as petroleum refineries and power plants that use prior-art ACHE fan drives has been negatively affected by the poor reliability and right-angle drive system. The industries also discovered that belt drive and gearbox maintenance is a major expense in the life-cycle cost. Prior art motors were also prone to failure because of incorrect high pressure water spray. “Duty cycles for ACHE fan drives are extremely high due to extreme humidity, icing and dirt conditions, wind shear, water washing by operators (motors not being sealed can be sprayed with water to cool on hot days) and mechanical drive requirements.
Some end users spray water directly onto the ACHE cooling system in an effort to increase cooling performance on hot, process-limiting days. In addition, because fan blades may become “fouled” Many end users water-wash the ACHE system in order to maintain cooling performance. Directly exposing an ACHE system with high-pressure water spray may cause premature maintenance or failure of system components. This is especially true since lubrication system are not sealed and therefore allow water to penetrate. The efficiency and production rate is highly dependent on the ACHE cooling system’s ability to remove heat.
The single-speed fan drives of the past have other drawbacks. The fan being operated continuously at 100% speed can cause icing in the cooling tower when it is cold. Fan windmilling is another drawback. This occurs when the tower’s updraft forces cause the fan to turn in reverse. “Gearboxes used in prior art fan drives do not allow windmilling because of the limited lubrication available in reverse. In most cases, the gearboxes are equipped with anti-reverse mechanisms.
Such systems use lagging feedback loops that result in fan speed oscillation, instability and speed hunting. This consumes large amounts of energy during abrupt speed changes and inertial changes which results to premature wear and failure of gear train parts designed for single speed, omni-direction operation. These systems use lagging feedback that results in fan speed oscillations, instability, and speed hunting. This consumes large amounts of power during abrupt speed changes, inertial changes, and premature wear of gear train components that are designed for a single speed, omnidirectional operation.
In prior art variable-speed fan systems, fan speed was controlled by the temperature of the basin. The fan speed increases according to an algorithm when the temperature of the basin exceeds the temperature set point. This is done to cool down the water in the basin. After the set temperature for the basin has been reached, the fan speed is reduced in accordance with the algorithms. Motors and gearboxes operate without any knowledge of cooling tower performance, and only in relation to the set temperature of the basin. This results in large fan speed swings where the fan is cycling from the minimum fan speed up to the maximum fan speed within a short time. The large speed swings at maximum fan acceleration use significant amounts of power.
The lubrication system and the gear mesh design of typical prior art gearboxes indicate that they are designed to rotate in one direction. These gearboxes weren’t designed to operate in reverse. Prior art gearboxes have been modified to add additional lube pumps to allow reverse rotation due to the design and functionality of the oil slinger system, which only works in one direction. These lube pump are usually electric, but they can be other designs. Gear mesh in the gearbox can also be a factor in limiting reverse rotation, as the load on the mesh cannot support the same design load as in forward rotation. The modified gearboxes were only able to operate at low speeds in reverse for a maximum of two minutes. In colder climates, end users who need to reverse the rotation of the cooling system on cold days for deicing have reported many failures in the gearbox drivetrain system. Secondary damage has also been reported including the collapse of the cooling station. The majority of operators, including an electrician, have to manually reverse each cell. The gearbox is designed to rotate in one direction at 100% fan speed. Fan braking, geartrain inertia, and variable speed duty can accelerate wear on the gearbox.
Due to their bearing design, even with a lubrication system, the prior art gearboxes can only operate at very low speeds. They are also limited to a maximum reverse time of two minutes. In most cooling towers the fans run continuously at 100% speed. The additional cooling caused by the fans running at 100% fan speeds can cause the cooling towers to freeze, which could lead to the collapse of the cooling tower. Cooling tower operators have used two-speed motors as a prior art to drive fans. In this prior art configuration, a two-speed motor would be continuously jogged forward and backward in an attempt to de-ice the cooling tower. In some cases the gearboxes may be operated past the two-minute interval to de-ice the tower. This technique can cause damage to the tower and gearbox. The fan’s mechanical system and ice will form if the motors are turned off in order to prevent the towers from freezing. A technique that has been used in the past is to use fire hoses to draw water out of the cooling tower basin at night. This is a dangerous technique that often results in injuries to personnel.
Variable speed fan systems are not widely used.” In the hopes of reducing energy consumption, VFDs are being applied more to fan gearboxes and induction motors. These modifications, however, require the installation of motors rated for invertors and fan gearboxes that are more robust to accommodate inertial loads for which they were not designed. DOE (Department of Energy), reports that such applications average 27% energy savings. The savings are directly proportional with the fan laws, as opposed to motor efficiency which, for an induction, drops significantly in part-load operations.
Current cooling towers do not typically use expensive condition monitoring equipment with questionable reliability, which is not widely accepted by end users. In prior art fan systems, vibration safety is achieved by placing vibration switches near the motor on the ladder frame. A vibration switch of this type is shown in FIG. 8A. 1. These vibration switches do not have any external monitoring or signals. They are just on/off switches. These vibration switches are not reliable and poorly maintained. These vibration switches do not provide any information or signals regarding the integrity of fan systems. It is therefore impossible to identify the cause or source of vibrations. These vibration switches can also malfunction or perform poorly and need to be tested frequently to ensure they are functioning. These switches are not reliable and do not detect blade failures. This is a serious safety concern. In alternative configurations, vibration sensors have been mounted on the gearbox or within it. These vibration sensors lack the filtering and fidelity of vibration signals required for condition monitoring or system shutdown. “Static fan balancing is the norm in prior art fan balancing.
In multi-cell cooling prior art systems, which utilize a number of fans with gearboxes, each fan operates independently at 100% or variable speed, controlled independently by the algorithm. Cooling towers typically have one design point, such as maximum daytime temperature or maximum wet bulb temperature. These cooling towers run the fans at 100% constant state in order to meet the design conditions of maximum hot day temperatures and maximum wet-bulb temperatures, regardless the environmental conditions or process load.
The current practice (Cooling Tower Institute, American Society of Mechanical Engineers), attempts to measure cooling tower performance with a precision which is considered unpractical for a system that constantly changes in temperature. The vast majority of refinery operators do not measure performance, and wait far too long to fix and restore cooling tower performance. Some end-users operate their cooling towers until they fail. Some users test cooling towers on a regular basis to ensure they are performing as expected. This is usually done when the cooling tower exhibits a cooling performance issue. These tests are expensive and time-consuming, and normalize test data according to the tower design curve. These tests also do not produce any trending data, load data, or long-term information to determine performance, maintenance, and service criteria. When the cooling tower fill becomes clogged, for example, there is an excessive energy waste. The cooling tower fans are not able to perform as effectively when the cooling fill is clogged. Reduced cooling can negatively affect the process, resulting in a degraded quality of product or throughput. Unscheduled production interruptions and downtime can be caused by poor cooling tower performance. It is common for end users to operate cooling tower systems incorrectly by increasing the electrical power of the fan motors in order to compensate for a clogged cooling tower, or to increase water flow to the cooling tower to increase cooling. However, the corrective action should be to replace the filling. Incorrect cooling tower operation can result in incorrect cooling and have many negative effects, such as decreased cooling capacity, low reliability, excessive energy use, poor plant performance and decrease in production.
The reliability of variable load wet cooling towers and ACHE systems, as well as their performance, must be managed and improved to ensure refinery safety and production.
The global industrialization has accelerated the demand for HVAC. The demand for HVAC is expected to grow as the per capita income of developing countries increases, and established markets invest in energy-efficient HVAC systems using environmentally friendly refrigerants. This will help them comply with new regulations and receive financial incentives. Intelligent Building Systems are being installed in sports complexes, offices, malls, and skyscrapers. These systems actively monitor and manage the building’s heating, cooling, and humidity under changing weather conditions. A properly functioning HVAC system is directly linked to the health and safety of occupants, building integrity and comfort. Many HVAC systems use centrifugal fan which has less than desirable performance and balance, noise level, and energy efficiency.
What is needed is a direct drive, load bearing system that will eliminate the problems and inefficiencies associated with prior art drive systems.
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