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Edited by John C. All Rights Reserved This book or any part thereof must not be reproduced in any form without written permission of the publisher. Foreword Although the worlds total fresh water supply is abundant, some areas have water usage demands that are heavily out of balance with natural replenishment. Conservation and efcient reuse of this precious and versatile resource are mandatory if such areas are to achieve proper development. And, the need for water conservation does not limit itself only to arid regions.
Recognition of the detrimental environmental impact of high temperature water discharge into an estuary, whose inhabitants are accustomed to more moderate temperature levels, makes one realize that the re-cooling and reuse of water, however abundant, conserves not just that important natural resourceit conserves nature as well.
One helpful means to that end is the water cooling tower. Those responsible for the specications, purchasing and operation of plant, station, or building cooling systems must consider many aspects beyond the primary requirement of dissipating unwanted heat. The following text is devoted to identifying the primary and peripheral considerations and offering approaches rened by some eighty years of experience in the cooling tower industry.
The goal is to assure the implementation of water cooling systems which will satisfy all design and environmental requirements with sound engineering and responsible cost. This manual is not intended to be all-encompassing and thoroughly denitive. The entire scope of cooling towers is too broad, and the technology far too advanced, to permit complete coverage in a single publication. Separate brochures by SPX Cooling Technologies, either existing or planned, cover individual topics in depth.
The intent herein is to provide a level of basic knowledge which will facilitate dialogue, and understanding, between user and manufacturer. Types of Towers. The Psychrometrics of Evaporation Factors Affecting Cooling Tower Performance Materials of Construction Maintaining Water Quality. Operation in Freezing Weather. Cold Water Basin Tower Framework. Water Distribution System Fan Deck Fan Cylinders Mechanical Equipment Supports Fill heat transfer surface.
Drift Eliminators Access and Safety Considerations Speed Reducers Drive Shafts Safety Considerations Motor Controls. Wiring System Design Cycling of Motors. Water Conservation. Visual Impact and Plume Control Adiabatic Air Precooling. Energy Reduction Energy Management and Temperature Control Noise Control Drift Reduction. Abnormal Operating Conditions.
Vibration Isolation. Free Cooling. Helper Towers. Extended Oil Fill and Gauge Lines Mechanical Equipment Removal Devices Prevention of Basin Freezing. Filtering Systems Fan Brakes and Backstops. Air Inlet Screens Distribution Basin Covers Vibration Limit Switch. Fire Protection, Prevention and Control. Tower Preparation for Test Instrumentation for Test Operating Conditions During Test Conducting the Test Evaluation of Test Data Covering Specication Tower Orientation and Site Services.
Economic Evaluation Parameters. Contractual Information Comparing Capability of Proposed Towers Cleaning and Biological Control. Cooling Tower Basics A. Although this heat is usually transferred to a cool, owing volume of water, nal rejection is always to the atmosphere and, invariably, is accomplished by some form of heat exchanger.
Many of those terminal heat exchangers are not easily recognized as such because they are better known as creeks, rivers, lakes, etc. The natural process of evaporation makes them very effective heat transfer mediums, although somewhat inefcient due to their limited surface area and their total dependence upon random winds.
Although the happy man depicted in Figure 1 may not completely understand the principle of evaporation, he is intuitively making use of this most ancient form of natural cooling. Primeval, perspiring mankind depended upon natural breezes to accelerate this evaporation process, and was grateful when they came.
At some point in that distant past, however, hands began to manipulate broad leaves to create an articial breeze and the basic concept of a cooling tower was unknowingly founded. Eons later, the advanced technology which allows Mr. Figure 1 to revel in a mechanically-produced ow of air made nite development of the cooling tower practicable. Not all types are suitable for application to every heat load conguration. Understanding the various types, along with their advantages and limitations, can be of vital importance to the prospective user, and is essential to the full understanding of this text.
The small atmospheric tower depicted in Figure 2 derives its airow from the natural induction aspiration provided by a pressure-spray type water distribution system. Although relatively inexpensive, they are usually applied only in very small sizes, and are far more affected by adverse wind conditions than are other types. Their use on processes requiring accurate, dependable cold water temperatures is not recommended and as such has become rarely used. Figure 2 Atmospheric spray tower.
Conversely, the atmospheric type known as the hyperbolic natural draft tower Figs. Air ow through this tower is produced by the density differential that exists between the heated less dense air inside the stack and the relatively cool more dense ambient air outside the tower. Typically, these towers tend to be quite large , gpm and greater , and occasionally in excess of feet in height. Their name, of course, derives from the geometric shape of the shell.
Although hyperbolic towers are more expensive than other normal tower types, they are used extensively in the eld of electric power generation, where large unied heat loads exist, and where long amortization periods allow sufcient time for the absence of fan power and mechanical equipment maintenance costs to recoup the differential cost of the tower.
The synfuels industry also potentially generates heat 8. Figure 3b Crossow natural draft tower. Thus their thermal performance tends toward greater stability, and is affected by fewer psychrometric variables, than that of the atmospheric towers. Section V-F Mechanical draft towers are categorized as either forced draft Fig.
Figure 4 Forced draft, counterow, blower fan tower. Forced draft towers are characterized by high air entrance velocities and low exit velocities.
Accordingly, they are extremely susceptible to recirculation Sect. I-E c and are therefore. Furthermore, located in the cold entering ambient air stream, forced draft fans can become subject to severe icing with resultant imbalance when moving air laden with either natural or recirculated moisture. Usually, forced draft towers are equipped with centrifugal blower type fans which, although requiring considerably more horsepower than propeller type fans, have the advantage of being able to operate against the high static pressures associated with ductwork.
Therefore, they can either be installed indoors space permitting , or within a specially designed enclosure that provides signicant separation between intake and discharge locations to minimize recirculation. Induced draft towers have an air discharge velocity of from 3 to 4 times higher than their air entrance velocity, with the entrance velocity approximating that of a 5 mph wind.
Therefore, there is little or no tendency for a reduced pressure zone to be created at the air inlets by the action of the fan alone.
Cooling Tower Fundamentals
The former is the preferred method, serving to isolate vibration originating throughout the cooling tower structure, whereas the latter method tends to isolate only the vibration occurring at tower mechanical equipment operating frequencies. When isolating the entire tower, all pipe, conduits, and other components solidly connected to the tower must have vibration damping capability. Vibration isolation systems are rated in terms of efficiency or transmissibility. Efficiency is the percentage of the vibration force prevented from being transmitted. For a specific isolation system and deflection, isolation efficiency increases with the frequency of the disturbance. Thus, if the vibration isolation system for a given machine is designed for the lowest disturbing frequency at an acceptable efficiency, the isolation efficiency for higher speed elements in the same machine will be greater.
Marley Cooling Tower Fundamentals