Patent Application
20110227236
The present invention relates to an apparatus and method for an air bypass system for a natural draft cooling tower that employs a wet heat exchanger, a direct dry heat exchanger or an indirect dry heat exchanger to extract heat from a heated fluid, which is usually liquid or steam. The aforementioned cooling tower operates by natural draft which utilizes air buoyancy via a tall chimney. The extracted heat produces warm air from and naturally rises due to the density differential to the cooler outside ambient air.
Cooling towers are heat exchangers of a type widely used to emanate low grade heat to the atmosphere and are typically utilized in electricity generation, air conditioning installations and the like. In a natural draft cooling tower for the aforementioned applications, airflow is induced via hollow chimney-like tower by the density difference between cool air entering the bottom of the tower and warm air leaving the top. This difference is due to heat transfer from the fluid being cooled, which is passed through the interior of the tower. Cooling towers may be wet or dry. Dry cooling towers can be either “Direct Dry,” in which steam is directly condensed by air passing over a heat exchange medium containing the steam or an “Indirect Dry” type natural draft cooling towers, in which the steam first passes through a surface condenser cooled by a fluid and this warmed fluid is sent to a cooling tower heat exchanger where the fluid remains isolated from the air, similar to an automobile radiator. Dry cooling has the advantage of no evaporative water losses. Both types of dry cooling towers dissipate heat by conduction and convection and both types are presently in use. Wet cooling towers provide for direct air contact to a fluid being cooled. Wet cooling towers benefit from the latent heat of vaporization which provides for very efficient heat transfer but at the expense of evaporating a small percentage of the circulating fluid.
In addition to types of cooling tower designs described above, cooling towers can be further classified as either cross-flow or counter-flow. Typically in a cross-flow cooling tower, the air moves horizontally through the fill or packing as the liquid to be cooled moves downward. Conversely, in a counter-flow cooling tower air travels upward through the fill or packing, opposite to the downward motion of the liquid to be cooled.
In a direct dry cooling tower, the turbine steam exhaust is condensed directly in an air-cooled condenser. Approximately five to ten times the air required for mechanical draft evaporative towers is necessary for dry cooling towers. This type of cooling is usually used when little or no water supply is available. This type of system consumes very little water and emits no water vapor plume.
To accomplish the cooling required, the condenser requires a large surface area to dissipate the thermal energy in the gas or steam and presents several problems to the design engineer. It is difficult to efficiently and effectively direct the steam to all the inner surface areas of the condenser because of nonuniformity in the delivery of the steam due to system ducting pressure losses and velocity distribution. Therefore, uniform steam distribution is desirable in air cooled condensers and is critical for optimum performance. Therefore it would be desirous to have a condenser with a strategic layout of ducting and condenser surfaces that would ensure an even distribution of steam throughout the condenser, while permitting a maximum of cooling airflow throughout and across the condenser surfaces.
Another problem with the current air cooled condensers is the expansion and contraction of the ducts and cooling surfaces caused by the temperature differentials. Pipe expansion joints may be employed at critical areas to compensate for the thermal movement. A typical type of expansion joint for pipe systems is a bellow which can be manufactured from metal (most commonly stainless steel). A bellow is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections. In all but the smallest of applications, branching of the steam ducting is required to distribute the steam to the various coil sections of the condenser. The very nature of branching breaks the steam flow into different directions which necessarily introduces thermal expansion in different directions. These expansion accommodating devices are expensive. Therefore it would be additionally desirous to have a condenser arrangement in which the thermal expansion and contraction is simply and inexpensively managed.
The natural draft cooling tower typically has a hollow, open-topped shell of reinforced concrete with an upright axis of symmetry and circular cross-section. The thin walled shell structure usually comprises a necked, hyperbolic shape when seen in meridian cross-section or the shell may have a cylindrical or conical shape. Openings at the base of the tower structure enable ingress of ambient air to facilitate heat exchange from the fluid to the air. Forced draft cooling towers are also known, in which the airflow is produced by fans. These devices usually do not incorporate a natural draft shell because the fans replace the chimney effect of the natural draft cooling towers. However, forced draft fans may be incorporated in a natural draft design to supplement airflow where the density difference described above is not sufficient to produce the desired airflow.
It is known that improving cooling tower performance (i.e. the ability to extract an increased quantity of waste heat in a given surface) can lead to improved overall efficiency of a steam plant's conversion of heat to electric power and/or to increases in power output in particular conditions. Cost-effective methods of improvement are desired. The present invention addresses this desire. Equivalent considerations can apply in other industries where large natural draft cooling towers are used.
Additionally, large natural draft cooling towers are high-capital-cost, long-life fixed installations, and it is desirable that improvements be obtainable without major modifications, particularly to the main tower structure. The method and apparatus of the present invention are applicable to the improvement of existing natural draft cooling towers, as well as to new cooling towers.
In cooler weather the return temperature of a fluid from the cooling tower and/or freezing a fluid in the heat exchanger is a major concern. When the airflow has the capacity to exchange more heat than desired the airflow must be reduced. Airflow dampers are known to be used is series with heat exchangers. The dampers may be throttled to restrict the airflow. However, even in the wide open position a pressure loss through the damper occurs. This pressure loss reduces the total airflow and thus the cooling capacity of the tower.
Additionally, due to temperature and humidity extremes, a natural draft cooling tower may extract too much heat energy out of the heated liquid or have the liquid to be cooled freeze up. For example, a dry cooling tower may extract too much thermal energy away from the heated liquid condensate, which would require extra heating energy from a boiler or heat source to reheat the liquid back to its optimal temperature, thus lowering the system's efficiency. A wet tower on the other hand is susceptible to ice formation in cold weather. In particular ice may form and build up in the fill and cause structural damage to the fill and/or the supporting structure.
Therefore it would desirous to have an economical, efficient natural draft cooling tower in which the cooling airflow could also be controlled. It would be also desirous to have a way to mix ambient air with the cooling air to better regulate the entire cooling system.
Embodiments of the present invention advantageously provides for an air bypass system and method for a cooling tower, which can be applied to dry or wet cooling towers. An embodiment of the invention includes a natural draft cooling tower that cools an industrial fluid, comprising a tower having a perimeter that extends vertically about a vertical axis through which an airstream flows and a heat exchanger disposed proximate said tower, wherein, the industrial fluid and airstream flow there through. It further includes a chimney section and a base section, wherein said base section comprises a first airflow inlet at a first vertical position along the vertical axis and a second airflow inlet located at second vertical position along the vertical axis.
Another embodiment is for a natural draft cooling tower that cools an industrial fluid, comprising a tower having a perimeter that extends vertically about a vertical axis and a first airflow inlet at a first vertical position along the vertical axis providing a first airflow. It further includes a heat exchanger positioned adjacent to said first airflow inlet such that the first airflow enters and passes through said heat exchanger prior to entering said first air inlet and a second airflow inlet located at second vertical position along the vertical axis providing a second airflow to be mixed with said first airflow.
Another embodiment of the present invention is for a method for cooling an industrial fluid using a natural draft cooling tower, the method comprising flowing the industrial fluid to be cooled through a heat exchanger and flowing a first airflow through a first inlet at a first vertical position and over said heat exchanger to induce heat exchange and flowing a second airflow through a second airflow inlet located at a second vertical position. The method further includes mixing said first airflow and said second airflow as said first airflow exits said heat exchanger.
An additional embodiment of the present invention is for a method for cooling an industrial fluid using a natural draft cooling tower, the method comprising flowing the industrial fluid to be cooled through a heat exchanger, wherein the heat exchanger is positioned adjacent a first airflow inlet at a first vertical position to induce heat exchange and flowing a second airflow through a second airflow inlet located at a second vertical position. The method further includes mixing said first airflow and said second airflow as said first airflow exits said heat exchanger.
Another embodiment is for the system, having the means for cooling an industrial fluid using a natural draft cooling tower and the means for flowing the industrial fluid to be cooled through a heat exchanger. The system also has the means for flowing a first airflow through a first inlet located at a first vertical position means for flowing said first airflow through said heat exchanger to induce heat exchange on the industrial fluid via said airflow and the means for flowing a second airflow through a second inlet and further means for mixing said first airflow and a second airflow inside a cooling tower structure.
There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the disclosure itself will be better understood by reference to the following description of various embodiments of the disclosure taken in conjunction with the accompanying figures.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and show by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized, and that structural, logical, processing, and electrical changes may be made. It should be appreciated that any list of materials or arrangements of elements is for example purposes only and is by no means intended to be exhaustive. The progression of processing steps described is an example; however, the sequence of steps is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps necessarily occurring in a certain order.
A separate cooling water supply is provided to heat exchanger 6 via a duct 8 and exits at an elevated temperature via a duct 9, being pumped by cooling water pumps 10. In some installations, a large supply of water is available from a lake, river or artificial cooling pond for use as cooling water. However, in cases where supply is not available, cooling water may be directly recirculated as shown in
Wet or evaporative cooling towers are heat exchangers of the type in which a liquid as shown in
Now, with reference to
As with any physical body in which goes through temperature variations, it will expand or contract in accordance with its temperature. An advantage of using the peripheral manifold in a big loop with a fixed point center riser arrangement is that its thermal dilatation is purely radial and there is no need of bellows. Maximum radial expansion is approximately 1 inch. This movement is introduced at the top of the coil which is purposely not constrained at the top from radial movement as the top of the bundles are only connected to the steam box and the peripheral duct. Because the coils are so tall, the radial movement will induce only a slight inclination of the coils. Not only does this save cost in construction by not having to employ bellows, but the bellows will not become a point of failure for the system, nor will they need to be replaced at a regular maintenance interval. An additional advantage of the above arrangement is that it allows an engineer to design an easy and inexpensive cleaning system that can be hung on a rail located on the perimeter of the cooling annular ring and above the bundles owing to the fact the tube bundles are arranged in a circumferentially oriented outward face as opposed to a pleated or zigzag arrangement.
Turning to
As can be seen, the bottom of the base stratum section 54 is at ground level and has air inlet with an airflow regulator installed. In this example, the airflow regulator is shown as louvers 55, which translate between an open and closed position to control airflow through the cooling structure 56. The louvers discussed throughout the present application can be replaced with any air flow regulation device. For example, the louvers can be replaced with roll up doors, hinged doors, sliding doors or any variable structure to limit airflow through an opening. An optional access door 59 is also shown. The chimney section depicted is cylindrical; however, it can be any shape that allows for air efficient traversal through the chimney section. For example, the chimney section can be in the shape of a hyperboloid, which is the shape most people associate with nuclear power generation stations.
As the steam traverses through the finned tube bundles 48, it cools and reverts back into its liquid form. The liquid reaches the bottom of the finned tube bundle 48 into to a collector 49 and the liquid leaves via water return 64, as shown in
As illustrated in
The present embodiment has many advantages. For example, the louvers provide an inexpensive control system. The louvers are less costly than isolating valves which have to be installed on the steam ducting to neutralize the exchange surface by segments or partitions. The present invention needs a relatively low amount of louvers, approximately 50% of the face area of the bundles need to be covered with louvers to be effective. Additionally, the actuators of the louvers are located on ground level enabling an easy maintenance. However, the air bypass could be located above the tube bundles and have similar air flow regulating characteristics.
Turning now to
Turning now to
In
In
Now turning now to
In
The louvers as described in the aforementioned description and figures may be replaced by other means to regulate air flow such as but not limited to roll up doors, hinged doors, sliding doors, or butterfly valves.
The processes and devices in the above description and drawings illustrate examples of only some of the methods and devices that could be used and produced to achieve the objects, features, and advantages of embodiments described herein and embodiments of the present invention can be applied to indirect dry, direct dry and wet type heat exchangers. Thus, they are not to be seen as limited by the foregoing description of the embodiments, but only limited by the appended claims. Any claim or feature may be combined with any other claim or feature within the scope of the invention.
The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.
