In a relatively recent article on flare tower safety, the author pointed out that “Operating personnel often do not consider flare systems to be as important as other plant equipment. This issue is compounded by the fact that flares are usually located far from the operating plant, leaving them out of sight and, often, out of mind.” (1) If something like a flare tower, which is very visible, especially at night, can become out of mind to plant personnel, what does that say about cooling towers and other cooling system components? Numerous preventive measures are available during cooling system design and operation to establish and maintain reliability and efficiency. In Part 1 of this series, we will examine some of the most important components of cooling towers, and from that will build upon issues that can affect cooling system performance and operation. One of the later installments will address closed cooling water systems.
Important Cooling Tower Design Fundamentals
A large industrial plant such as a refinery, petrochemical facility, steel mill, etc., will have dozens if not hundreds of water-cooled heat exchangers to control various processes. While some large heat exchangers such as steam surface condensers may be on once-through cooling, many cooling systems are open-recirculating design that have a cooling tower as the core heat discharge process. Figure 1 outlines the basic schematic of a cooling system with a cooling tower at its heart.
Figure 1. Schematic of a cooling system with an induced-draft cooling tower. (2)
The bulk of heat transfer (typically 60% to 90% depending on ambient conditions and other factors) in a cooling tower comes from evaporation of a small portion of the recirculating water. Virtually all cooling towers contain some type of “fill” to enhance air/water contact and optimize the liquid-to-gas (L/G) ratio in the tower. This reduces the size and material/operational costs of the tower and of auxiliary equipment such as recirculating pumps and fans. Proper fill selection (and correctly designed water treatment programs, as we will explore in subsequent installments) are critical to maintain fill efficiency and reliability.
Early cooling towers had wooden splash fill; a series of staggered slats below the water spray or distribution nozzles.
Figure 2. General schematic of early wooden splash fill in a crossflow air pattern. (2)
Water impinging on the slats breaks into small droplets that increase the surface area. Splash fill is common for crossflow towers, and the technology has been considerably improved, with a modern design shown below.
Figure 3. A modern splash fill arrangement.
Splash fill may be the only choice in cooling towers where the water has a high fouling tendency, but in most towers film fill is the preferred material, as it enhances air-water contact. Typical film fills are made of PVC per low cost, durability, good wetting characteristics, and inherently low flame spread rate. (3) Numerous designs are available. The choice of flow configuration and the spacing between the fill sheets (flute size) must be evaluated carefully and are dependent upon the projected quality of the recirculating water. Figures 4-7 below (courtesy of Brentwood Industries) show a progression of various film fill configurations moving from lower efficiency (and corresponding low fouling potential) to high efficiency and higher fouling potential.
Figure 4. Vertical Flutes (VF).
Figure 5. XF Stand-off.
Figure 6. Offset Flutes (OF).
Figure 7. Cross-Flutes (CF).
Selection of the correct fill offers a classic example of preventive design. The following abridged table, with data taken from Reference 4, outlines general guidelines for several of the configurations shown above.
Table 1: Fill Section Based on Water Quality (4)
“Good” biological control represents oxidizing biocide feed, with total aerobic bacteria (TAB) maximum plate counts not exceeding 100,000 cfu/ml (colony forming units) with minimal slime formation on heat transfer surfaces.
“Poor” microbiological control implies minimal or no microbiological control, or control subject to significant disruption, with average TAB plate counts consistently over 100,000 cfu/ml.
Values listed represent concentrations of light, soluble oils. Heavy oils and greases would require a specific recommendation on a job-to-job basis.
Values listed require limits on the concentrations of light, soluble oils to 5 ppm or less and 0 ppm on heavy oils & greases.
Even this abridged data clearly shows the tighter impurity guidelines for high efficiency fills (CF and XF designs) versus the lower efficiency VF types. Additional notes in this technical bulletin mention the influence of other impurities including microbiological nutrients such as ammonia compounds and sugars. We will examine microbiological fouling in greater detail in Part 2.
Additional Cooling Tower Maintenance Items
Other critical cooling tower equipment includes:
Water spray/distribution system
Circulating pumps
Fans and gear drives
Drift eliminators
Water Distribution System
Water distribution for a counterflow tower is typically provided from a header/lateral spray system that resides a few feet above the fill.
Figure 8. Schematic of an induced-draft, counterflow cooling tower. (2)
The headers, laterals, and nozzles are designed to provide an even distribution of water to the fill to minimize “channeling.”
Figure 9. Photo of several laterals and spray nozzles in a counterflow tower.
Obviously, failure or plugging of spray nozzles could cause flow maldistribution, and whenever opportunities permit, maintenance personnel should inspect nozzles for damage and fouling.
In crossflow towers, the return water is typically discharged onto a distribution deck with uniformly spaced target nozzles within the deck that allows the water to feed by gravity into the air passing perpendicularly.
Figure 10. Schematic of an induced-draft crossflow cooling tower. (2) Return water is discharged onto distribution decks with a uniform pattern of nozzles, such that gravity provides the water pressure.
Figure 11 illustrates a small portion of a crossflow cooling tower deck with water draining through several penetrations.
Figure 11. Water flowing through several penetrations of the cooling tower deck.
Regardless of the cooling tower type, the fill requires uniform water distribution to minimize channeling. Channeling by itself will reduce tower efficiency, but it can also establish low-flow locations that allow increased deposition and formation of microbiological colonies. For crossflow towers, plugging of the nozzles by solid materials or algae can negatively influence water distribution.
Circulating Pumps
Recirculating systems are typically designed with multiple pumps so that the water flow rate can be adjusted per seasonal temperature changes, although with multi-cell cooling towers, cells can be placed in or removed from service to follow heat load. As with other pumps in the plant, a preventive inspection and repair program is important to maintain pump reliability.
Fans
Most large cooling towers are of the induced draft style where the multi-bladed axial fans pull air through the tower.
Figure 12. An ID fan at the top of a cooling tower cell.
Important aspects of fans beyond size and motor horsepower include fan speed and blade pitch. Air flow can stall if the fan pitch settings are not correctly configured for the fan’s RPM. Regular monitoring and maintenance are important. Fans may become unbalanced and misaligned from the accumulation of deposits that exit with the exhaust plume. Fan blade leading edges may become eroded due to constant impact with drift droplets in towers where drift is an issue. Gearboxes are another item that require regular inspection and lubricant monitoring.
A not uncommon arrangement is dual-speed fan control, or perhaps even variable frequency drive (VFD) control. Thus, rather than placing a cell or cells in or out of service to adjust for load or ambient air temperature changes, it may be possible to adjust the fan speed.
Drift Eliminators
The interaction of air and water in the tower generates many fine droplets that can potentially exit the tower in the plume. The common term for this loss is “drift.” Drift discharge is problematic for three reasons. First, solids within the droplets can deposit on induced-draft fan blades and gradually impact performance. Secondly, plant air emissions regulations often include cooling tower discharge. A facility may be in violation of discharge guidelines from the solids entrained in the droplets. Thirdly, drift droplets are considered a vector for the transmission of legionella bacteria, the cause of legionnaire’s disease, an illness that can be fatal to those with compromised immune systems. Accordingly, cellular-type drift eliminators are standard cooling tower items. They collect water by impingement and allow the water to drain back into the wet section of the tower.
Figure 13. A modern high efficiency drift eliminator design. Photo courtesy of Brentwood Industries.
Technology has advanced such that modern drift eliminators can reduce entrained moisture to less than 0.0005% of the recirculating water rate. To put that into perspective, the drift from a tower with a 100,000 gpm recirculation rate and 0.0005% drift would be 0.5 gpm.
Additional Operational/Maintenance Concerns
Cooling towers are superb air scrubbers, and many air-borne materials enter cooling systems to cause potential problems in tower fill, cooling system heat exchangers, and other equipment. (Cottonwood seeds are particularly notorius.) Common cooling tower design guidelines recommend a sidestream filter to remove suspended solids. Figure 14 illustrates two common filter locations.
Figure 14. At left is a common “kidney-loop” sidestream filter arrangement on a cooling tower basin. An alternate location is the recirculating pump discharge shown at the lower right. (2)
The table below outlines four of the most common side stream filter technologies.
Table 2. Side Stream Technologies
(Source: Side Stream Filtration for Cooling Towers (energy.gov)
Another maintenance issue is the potential for ice formation in northern climates. Icing can damage equipment and restrict air flow through towers. Plant personnel should work with the tower manufacturer to develop an operational program to control ice formation during the winter months. Rotating cells in and out of service and changes in fan speed may help in this regard.
Conclusion
This initial series installment outlined many of the most important components of a cooling tower. Well-designed operating procedures and regular maintenance are important for trouble-free operation. The next installments will examine in greater detail the methods needed to maintain reliability of cooling towers and other cooling system components. For those interested in plunging into greater detail, Reference 2 provides an expanded discussion of many of these issues. Also, the Cooling Technology Institute (www.cti.org) offers a wealth of material about cooling systems.
B. Karthikeyan, “Manage Changes to Flare Systems”; Chemical Engineering Progress, Vol. 116, No. 1, January 2020.
Water Essentials Handbook (Tech. Ed.: B. Buecker). ChemTreat, Inc., Glen Allen, VA, 2023. Currently being released in digital format at https://www.chemtreat.com/.
Buecker, B., and R. Aull, “Cooling Tower Heat Transfer Basics – Part 2”; Hydrocarbon Processing, August 2020.
“ACCU-PAC General Fill Selection Guidelines”; Brentwood Industries, March 2024.
Richard Aull
Richard Aull is president and principal engineer of Richard Aull Cooling Tower Consulting, LLC. He has been working in the cooling tower industry for over 40 years, with a specific interest in tower thermal design, performance rating, and analysis. Prior to starting his consulting business in 2017, he held technical positions within Brentwood Industries’ cooling tower business unit, first as R&D manager and lastly as director of application engineering.
Earlier in his career he held a variety of engineering positions within Research Cottrell’s Hamon Cooling Tower Division and the Ecodyne Cooling Tower Services Group. Rich is active in the Cooling Technology Institute (CTI) and has published technical papers and conducted seminars on a variety of cooling tower topics for the Cooling Technology Institute, Electric Power Research Institute, International Water Conference, IAHR Conference on Cooling Towers and Air-Cooled Heat Exchangers, India’s NTPC’s India Power Station O&M Conference, NTPC’s Global Energy Summit, and the American Society of Mechanical Engineers. Rich has B.S. and M.S. degrees in mechanical engineering from the New Jersey Institute of Technology focusing on thermodynamics, heat transfer, and fluid dynamics and is a registered Professional Engineer in the states of Pennsylvania, New Jersey, and Missouri.
Brad Buecker
Brad Buecker is president of Buecker & Associates, LLC, consulting and technical writing/marketing. Most recently he served as a senior technical publicist with ChemTreat, Inc. He has many years of experience in or supporting the power industry, much of it in steam generation chemistry, water treatment, air quality control, and results engineering positions with City Water, Light & Power (Springfield, IL, USA) and Kansas City Power & Light Company's (now Evergy) La Cygne, KS, USA, station. His work has also included eleven years with two engineering firms, Burns & McDonnell and Kiewit, and he spent two years as acting water/wastewater supervisor at a chemical plant.
Buecker has a B.S. in chemistry from Iowa State University with additional course work in fluid mechanics, energy and materials balances, and advanced inorganic chemistry. He has authored or co-authored over 250 articles for various technical trade magazines, and has written three books on power plant chemistry and air pollution control. He is a member of the ACS, AIChE, AIST, ASME, AWT, the Electric Utility Chemistry Workshop planning committee, and he is active with the International Water Conference and Power-Gen International.
In this advisory, we are going to demonstrate how hazardous, documented, service, repair, and troubleshooting recommendations have proliferated the fluid power industry, leaving unsuspecting persons vulnerable to possible injury or death. Unsafe service, repair, and troubleshooting recommendations are running rampant throughout the fluid power industry - and there is no end in sight!
In this advisory, we are going to demonstrate how hazardous, documented, service, repair, and troubleshooting recommendations have proliferated the fluid power industry, leaving unsuspecting persons vulnerable to possible injury or death. Unsafe service, repair, and troubleshooting recommendations are running rampant throughout the fluid power industry - and there is no end in sight!
Hydraulic systems must store fluid under high pressure. Three kinds of hazards exist: burns from the hot, high pressure spray of fluid; bruises, cuts or abrasions from flailing hydraulic lines; and injection of fluid into the skin. Safe hydraulic system performance requires general maintenance. Proper coupling of high and low pressure hydraulic components and pressure relief valves are important safety measures.
Hydraulic systems must store fluid under high pressure. Three kinds of hazards exist: burns from the hot, high pressure spray of fluid; bruises, cuts or abrasions from flailing hydraulic lines; and injection of fluid into the skin. Safe hydraulic system performance requires general maintenance. Proper coupling of high and low pressure hydraulic components and pressure relief valves are important safety measures.
Results-oriented organizations focus first on the quality and volume of production throughput, followed closely by the cost to produce the required quality and volume. This approach will improve reliability performance, which will drive manufacturing costs down.
Results-oriented organizations focus first on the quality and volume of production throughput, followed closely by the cost to produce the required quality and volume. This approach will improve reliability performance, which will drive manufacturing costs down.
It never ceases to amaze me that no matter what industry you are in or how big or small of a company you work for, success is dependent on the ability to find, attract, hire, manage, develop and retain the right people. I continue to see companies disproportionately dedicate more focus and investment into non-people issues such as technology or equipment than focusing on getting “the right people on the bus.” I haven’t quite figured out why, but I believe it could boil down to one of three reasons:
It never ceases to amaze me that no matter what industry you are in or how big or small of a company you work for, success is dependent on the ability to find, attract, hire, manage, develop and retain the right people. I continue to see companies disproportionately dedicate more focus and investment into non-people issues such as technology or equipment than focusing on getting “the right people on the bus.” I haven’t quite figured out why, but I believe it could boil down to one of three reasons:
Christer Idhammar of IDCON INC presents the implementation steps you need to take if you want to be successful in improving reliability and maintenance, sustain that improvement, and continue to improve after that.
Christer Idhammar of IDCON INC presents the implementation steps you need to take if you want to be successful in improving reliability and maintenance, sustain that improvement, and continue to improve after that.
The current economic climate dictates that cost management is a critical activity for many companies and their managers. Maintenance is very often seen as an area where cost cutting targets can be easily and quickly achieved. Many maintenance managers take the view that this type of philosophy always ends up with increased costs in the future. This is not true in many cases. 15 years of analysis and review of maintenance programs by the author shows that most maintenance departments are more reactive than they should be and because of this, they over spend and underperform.
The current economic climate dictates that cost management is a critical activity for many companies and their managers. Maintenance is very often seen as an area where cost cutting targets can be easily and quickly achieved. Many maintenance managers take the view that this type of philosophy always ends up with increased costs in the future. This is not true in many cases. 15 years of analysis and review of maintenance programs by the author shows that most maintenance departments are more reactive than they should be and because of this, they over spend and underperform.
Corporations throughout the world are losing billions of dollars in wasted project spending, and this waste is being carefully hidden from management and investors. A new global research report shows that one of the biggest contributing factors is the lack of alignment of projects with corporate strategy.
Corporations throughout the world are losing billions of dollars in wasted project spending, and this waste is being carefully hidden from management and investors. A new global research report shows that one of the biggest contributing factors is the lack of alignment of projects with corporate strategy.
Oh "Overall Equipment Effectiveness", I've heard about that before! Unfortunately, in many facilities, that's all OEE (Overall Equipment Effectiveness) is to the personnel. Something they heard of, talked about or read about. Many maintenance departments today still do not effectively utilize the OEE tool even though it's widely used among the world class companies.
Oh "Overall Equipment Effectiveness", I've heard about that before! Unfortunately, in many facilities, that's all OEE (Overall Equipment Effectiveness) is to the personnel. Something they heard of, talked about or read about. Many maintenance departments today still do not effectively utilize the OEE tool even though it's widely used among the world class companies.
It is often said that "what gets measured gets done". And getting things done, through people, is what management is all about. Measuring things that get done and the results of this effort is an essential part of successful management, but too much emphasis on measurements, or the wrong measurements may not be in your company's best interests.
It is often said that "what gets measured gets done". And getting things done, through people, is what management is all about. Measuring things that get done and the results of this effort is an essential part of successful management, but too much emphasis on measurements, or the wrong measurements may not be in your company's best interests.
With the increased globalization and with companies acting globally, the need for a common understanding of the indicators to measure maintenance and availability performance is increasing, and there is no doubt that this activity in a short period of time will be a part in a global standard for maintenance indicators. This is highlighted by the fact that COPIMAN (Technical Committee on Maintenance of the Pan American Federation of Engineering Societies) is joining the comparison effort.
With the increased globalization and with companies acting globally, the need for a common understanding of the indicators to measure maintenance and availability performance is increasing, and there is no doubt that this activity in a short period of time will be a part in a global standard for maintenance indicators. This is highlighted by the fact that COPIMAN (Technical Committee on Maintenance of the Pan American Federation of Engineering Societies) is joining the comparison effort.
This article has several related themes. The main purpose is to give an overview of the engineering education process, relating theory to practical application. As part of this overview, I express gratitude to the scientists, mathematicians, and engineers who have guided my own education. This education is the foundation of my engineering career, as my experiences demonstrate.
This article has several related themes. The main purpose is to give an overview of the engineering education process, relating theory to practical application. As part of this overview, I express gratitude to the scientists, mathematicians, and engineers who have guided my own education. This education is the foundation of my engineering career, as my experiences demonstrate.
It's important to find out if material flows are present or not throughout a bulk-processing facility; material cost savings and increased plant efficiency can offset an investment in monitoring. Most bulk solids processors can do this using low-cost acoustic emission-monitoring technology.
It's important to find out if material flows are present or not throughout a bulk-processing facility; material cost savings and increased plant efficiency can offset an investment in monitoring. Most bulk solids processors can do this using low-cost acoustic emission-monitoring technology.
Sizing electric motors correctly for hydraulic power units can save a sizable amount of money over the life of the equipment. If system pressure and flow are constant, motor sizing simply boils down to the standard equation: hp = QP / 1714EM
Sizing electric motors correctly for hydraulic power units can save a sizable amount of money over the life of the equipment. If system pressure and flow are constant, motor sizing simply boils down to the standard equation: hp = QP / 1714EM
The power industry’s operating and maintenance practices were held up to intense regulator and public scrutiny when on November 6, 2007, a Massachusetts power plant’s steam-generating boiler exploded and three men died. The Department of Public Safety’s Incident Report investigation determined that the primary cause of the Dominion Energy New England’s Salem Harbor Generating Station Unit 3 explosion was extensive corrosion of boiler tubes
The power industry’s operating and maintenance practices were held up to intense regulator and public scrutiny when on November 6, 2007, a Massachusetts power plant’s steam-generating boiler exploded and three men died. The Department of Public Safety’s Incident Report investigation determined that the primary cause of the Dominion Energy New England’s Salem Harbor Generating Station Unit 3 explosion was extensive corrosion of boiler tubes
I was asked recently to give a second opinion on the cause of failure of an axial piston pump. The hydraulic pump had failed after a short period in service and my client had pursued a warranty claim with the manufacturer. The manufacturer rejected the warranty claim on the basis that the failure had been caused by contamination of the hydraulic fluid. The foundation for this assessment was scoring damage to the valve plate.
I was asked recently to give a second opinion on the cause of failure of an axial piston pump. The hydraulic pump had failed after a short period in service and my client had pursued a warranty claim with the manufacturer. The manufacturer rejected the warranty claim on the basis that the failure had been caused by contamination of the hydraulic fluid. The foundation for this assessment was scoring damage to the valve plate.
You have four opportunities to trouble shoot centrifugal pumps and each opportunity can offer you a clue as to what is wrong with the pump. Let's take a look at each of these conditions:
You have four opportunities to trouble shoot centrifugal pumps and each opportunity can offer you a clue as to what is wrong with the pump. Let's take a look at each of these conditions:
