New Energy and Water Saving Technology to Reduce Cooling Tower Operating Costs

Abstract
The use of ozone as a maintenance treatment for cooling towers has good potential for operation and maintenance savings in the Federal sector. A small amount of ozone acts as a powerful biocide that decreases or nearly eliminates the need to remove quantities of water from the cooling tower in order to decrease the concentration of organic and
mineral solids in the system. Ozone treatment can also reduce the need for chemical additives added to the cooling tower water.

In a properly installed and operating system, bacterial counts are reduced, with a subsequent minimization of the buildup of biofilm on heat exchanger surfaces. The resulting reduction in energy use, increased cooling tower operating efficiency, and reduced maintenance effort provide cost savings as well as environmental benefit and
regulatory compliance with respect to discharge of wastewater from blow down.

Cooling towers associated with chillers for air-conditioning are good candidates for ozone application. Ozone may be a corrosion stimulant rather than an inhibitor, and this can be a factor in some circumstances. Nevertheless, it is easier to combat corrosion in a clean system than in one that is biologically and mineralogically fouled.

This Federal Technology Alert (FTA) provides detailed information and procedures that a Federal energy manager needs to evaluate most cooling tower ozone treatment applications. The New Technology Demonstration Program (NDTP) technology selection process and general benefits to the Federal sector are outlined. Ozone treatment, energy savings, and other benefits are explained. Guidelines are provided for appropriate application and installation. Two actual case studies are presented to give the reader a sense of costs and energy savings. Current manufacturers, technology users, and references for further reading are included for prospective users who have specific or highly technical questions not fully addressed in this FTA.

About the Technology
Ozone is a molecule consisting of three oxygen atoms and is commonly denoted O3. Under ambient conditions, ozone is very unstable and as a result has a relatively short half-life of usually less than 10 minutes. Ozone is a powerful biocide and virus deactivant and will oxidize many organic and inorganic substances. These properties have made ozone an effective chemical for water treatment for nearly a century. During the last 20 years, technological improvements have made smaller-scale, stand-alone commercial ozone generators both economically feasible and reliable. Using ozone to treat cooling tower water is a relatively new practice; however, its market share is growing as a result of water and energy savings and environmental benefits relative to traditional chemical treatment processes. Ozone treatment of cooling tower water is not feasible in all situations and hence traditional chemical treatment of cooling tower water is the only alternative.

A cooling tower functions to cool a circulating stream of water (see Figure 1). The tower acts as a heat exchanger by driving ambient air through falling water, causing some of the warmed water to evaporate (evaporation gives off heat–providing cooling), and then circulating cooler water back through whatever equipment needs cooling (such as a chiller condenser). Typically, chemicals such as chlorine and chelating agents are added to cooling tower water to control biological growth (called “biofilm”) and inhibit mineral build-up (called “scale”). The control of biofilm and scale is essential in maintaining cooling tower heat transfer efficiency. As the water volume in the tower is reduced
through evaporation and drift, the concentration of these chemicals and their byproducts increases. Cooling towers also pick up contaminants from the ambient air. To maintain chemical and contaminant concentrations at a prudent level, water is periodically removed from the system through a process called “blowdown”or “bleed off”. The
blowdown water and the water lost through evaporation and drift are replaced with fresh “make-up” water (which will also contain minerals and other impurities).

Blow down water must subsequently be discharged to a local wastewater treatment facility or discharged onsite to the environment. The blow down water typically contains little organic material, and the local wastewater treatment facility will charge extra sewage fees for accepting the water. These costs can be quite significant in the overall costs of operating a cooling tower. Discharge of the blow down water to the environment onsite is coming under increasing regulation due to stricter regulation of the contaminants typically found in blow down water. Ozone will dissipate quickly and not be found in the blow down water. This reduces the overall chemical load found in the discharged water, making it easier to comply with regulations.

Most cooling tower ozone treatment systems include the following components: an air dryer, air compressor, water and oil coalescing filters, particle filter, ozone injectors, an ozone generator, and a monitoring/control system. Ambient air is compressed, dried, and then ionized in the generator to produce ozone. Ozone is typically applied to cooling water through a side stream of the circulating tower water as is illustrated in Figure 2.

Field tests have demonstrated that the use of ozone in place of chemical treatment can reduce the need for blow down, and, in some cases where make-up water and ambient air are relatively clean, can eliminate it. As a result, cost savings accrue from decreased chemical and water use requirements and from a reduction of wastewater volume. There are also environmental benefits as fewer chlorine or chlorinated compounds and other chemicals are discharged.

There is also a belief within the industry (and some evidence) that under certain conditions ozone acts as a descaling agent. The premise is that ozone oxidizes the biofilm that serves as a binding agent adhering scale to heat exchange surfaces. When scale buildup on condenser tubes is reduced, higher heat transfer rates are achieved. Increasing
the condenser heat transfer rate will reduce the chiller head pressure, which then allows the chiller to operate more efficiently and consume less energy.

There is a growing number of manufacturers and distributors of ozone equipment in the United States, and the use of this technology is encouraged by several major electric utilities and by electric utility and cooling tower associations. Each new application of ozone for cooling tower water treatment increases understanding of its overall
effectiveness and its applicability under differing physical conditions. The technology has had both success and failure.

Source – Spartan Water Treatment – More information on the criteria for applicability and the potential for the use of this technology in the Federal sector click here.

 

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Founded in Cape Town, January 2002, Wassertec has become the leader in ozone and ozone generation in Southern Africa.

From day one, our vision has been to design and manufacture the highest quality ozone generation systems primarily for the wine and bottled water industries. We believe that by taking care of the quality, the rest will take care of itself.
By collaborating with highly competent electrical engineers and industrial software developers, we have, over the years, created what we believe to be the best ozone systems currently available in their class.
From small beginnings we have grown the company and product line to become the leading manufacturer of ozone equipment in South Africa. Our specialised Bright Blue systems set the standard for ozone in the bottling industry.

Ozone Generation Specialists

With installations in nine African countries and clients such as Coca Cola, SAB and Distell, Wassertec are perfectly positioned to become your partners in ozone.

We not only design and manufacture our Ozone generation systems to the highest quality and safety standards, but we also stock all components at our Cape Town offices – ensuring rapid replacement of spares and minimal downtime.

If you are looking for high quality Ozone Generators, with backup and service to match, you’re in the right place. Welcome to Wassertec.