Technical Resources

In the design of a high performance cooling tower fill, many design features must be considered to produce optimum performance. This paper will show laboratory test data and detail the effect on fill performance of the following items: flute geometry (cross-corrugated, offset tube, vertical tube), cross-corrugated flute angle, sheet pitch (19 mm vs. 20 mm vs. 17 mm vs. 12 mm), microstructure (course, fine, none), material (PVC & polypropylene), module depth (12′ layers vs. 24″ layers vs. 48″ layers), and tip design (alternate tips vs. straight tips).

Evaporative precooling of air-cooled heat exchangers provides the thermodynamic advantages of water cooling towers with the reduced maintenance requirements of air-cooled heat exchangers. In areas where water conservation, cooling tower plume abatement, or water discharge permits are a problem, evaporative precooling of the air going to the heat exchanger can be the solution. This paper discusses the advantages of precoolers and presents some basic design considerations.

For many years PVC film fills have been the most popular choice of heat transfer media for use in cooling towers. Throughout this history, design features of these fills have continued to evolve from the first cross corrugated products through vertical flow fills to today’s popular combination designs. Some of these features are not obvious to the casual observer and if not chosen correctly can adversely affect tower performance, product cost, lifespan, or ease of installation. This paper traces the history of these fill designs while providing guidelines as to the proper fill selection.

The fouling of film fills in power plant cooling towers represents a major problem in loss of performance of the cooling tower and loss of efficiency of the power plant. The results of this loss of performance is higher energy consumption to drive the fans to move air through the cooling tower in mechanical draft towers. Higher fuel consumption in plant operations or reduced peak load output and the discharge of warmer water which poses environmental concerns to our rivers and lakes. This paper discusses the effects of fouling on cooling tower performance and the current knowledge to how this fouling may occur, industry practices of controlling cleaning and eliminating the problem using new film fill products.

Cooling tower drift is defined as the percent of circulating water flow that exits from the cooling tower fan stack in the form of fine water droplets and aerosols entrained in the exhaust air. For cooling tower drift tests, the CTI recommended Heated Bead Isokinetic (HBIK) procedure is the most commonly used procedure and is close to being accepted as a code by CTI, whereas regulators prefer the EPA Method 13A procedure. In theory both procedures (if properly operated, recovered and analyzed), should give the same results. This paper examines and compares the two-isokinetic methods and their proper operation, recovery and analysis so as to obtain accurate and repeatable results.

The testing services of Midwest Research Institute (MRI) were retained by Brentwood Industries, Inc. to conduct a series of 18 drift tests by using both the CTI recommended HBIK drift test procedure and the EPA Method 13A drift test procedure. The tests were conducted simultaneously using both test procedures on two types of Brentwood drift eliminators at two water loadings and several air velocities at the Ceramic Cooling Tower Company’s test facility located in Fort Worth, Texas.

The drift from the test cell was determined by isokinetically sampling a representative fraction of the test cell airflow above the drift eliminators. Lithium was added to the test cell circulating water prior to starting the series of tests to serve as an analysis tracer. Inductively coupled argon plasma spectroscopy (ICP), an extremely sensitive detection technique, was then used to measure the concentration of lithium in the circulating water and in the collected drift samples. The total drift rates were calculated from the ratio of the concentration of the lithium in the sampling train to the concentration of the lithium in the circulating water.

The CTI HBIK and the EPA 13A methods of isokinetic drift collection were found to yield nearly identical results in the series of tests.

Many utilities with power stations served by cooling towers are considering fill replacement due to deterioration of the original fill media. Often this allows an opportunity to reevaluate the unit’s thermal requirements and seek improvement on return cold water temperature, increasing unit performance. In the past, this meant specifying high efficiency, PVC packing as the most cost-effective path to improved thermal performance. Vendors’ submittals were typically evaluated based on capital cost plus energy cost savings due to more economical operation of the turbine/condenser allowed by the colder than originally specified return water temperature.

With recent discoveries of significant fouling in these highly efficient fills, utilities are incurring added costs to treat their circulating water to maintain their fills’ cleanliness. In a recent paper, one utility reported that their water treatment expenses have increased by a factor of six since the replacement of the original asbestos cement fill with high-efficiency PVC packing. This significantly reduced the economic advantage that the utility expected from the supplier’s guaranteed cold water temperature. New to the marketplace are anti-fouling fills that by design prevent or sharply reduce foulant buildup. However, this improvement in fouling resistance is accompanied by a modest drop in thermal performance. This may be more than offset by avoiding the high cost of aggressive water treatment required to maintain the cleanliness of higher performing fills.

This paper will describe an economic evaluation using the annual cost method that considers the difference in two repack alternatives: anti-fouling fills and standard, cross-corrugated fills. Differences in project capital costs, net plant heat rate, and water treatment costs will be computed. Using station specific economics, the least costly alternative is shown to be the use of lower efficiency anti-fouling fills with an existing water treatment program as opposed to high efficiency fills with an aggressive water treatment program.

There are many factors associated with the drift loss potential of a cooling tower. With the greater restrictions on drift emissions that are now required in many locales, it is important to know all of these factors to make sure that the drift loss of a tower is minimized. This paper will explore the various factors involved for both counterflow and crossflow cooling towers.

Using evaporative cooling systems saves resources, protects the environment, and provides economic benefits.

Film fill increases heat rejection and reduces air resistance, but also adds to the cost of cooling tower construction. Mechanically assembled film fill offers the same benefits with less labor costs while providing environmental benefits.

Not all cooling tower fills will meet your application’s performance and environmental requirements, so choose carefully. Here’s a primer to help you out.

This article highlights innovations in film and splash fill technology. These approaches offer new product selections that can be used in applications with poor water quality or process contamination and still provide the benefits of optimum thermal performance. These products are used in the more desirable counterflow towers and some can be employed in both counterflow and crossflow applications.