Chillers & Towers / Refrigeration

The Professor: Chemical-Free Cooling Tower Treatment

September 5, 2011
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Pure water is a rare commodity. Water, as we know it, contains many dissolved minerals. When evaporation occurs in a cooling tower, only the water evaporates; it exits the cooling tower as water vapor, but leaves the minerals behind to concentrate in the cooling tower’s water system.

The concentrations of these dissolved minerals gradually increase until a process called precipitation occurs. Precipitation happens when dissolved minerals such as calcium carbonate (limestone) reach a certain concentration and become solid, usually clinging to equipment and piping surfaces in the cooling tower. HVACR personnel refer to these solids as scale.

Tiny suspended particles exist in large quantities in all city water, or well water that is used for cooling tower or boiler makeup water. Once in the cooling tower water system, these suspended particles neither sink nor float because of their small size. They are transported by the flowing water.

The particles will concentrate during the evaporation process and be attracted to the equipment surfaces in the cooling tower. When the concentration is so great that the water can hold no more minerals, they are forced to find surfaces to precipitate to as a solid, scaling the equipment. This concentration and attraction of particles eventually becomes hard, equipment-damaging scale.

Now, a proprietary and patented technology has been developed by an engineering and research team. This chemical-free technology eliminates scale, inhibits bacterial growth, and inhibits corrosion in water purification (Figure 1).

How it Works

When the cooling tower water holding these small suspended particles passes through a water treatment module and is activated by a high-frequency electrical pulse field, the natural electrical static charge on the particle’s surface is removed.

In removing this surface charge on the suspended particles, they are now the preferred site for precipitation of minerals to occur, instead of the equipment surfaces. The suspended particles now act as seeds for precipitation of dissolved minerals. Thus, the hard scale is prevented from forming on the equipment’s surfaces and instead bonds to the tiny suspended particles in the water.

The minerals in the water now adhere to and coat the suspended particles. As more and more minerals bond to the suspended particles, they become heavier and can no longer suspend themselves in the water stream. They eventually make their way to the cooling tower’s basin as a harmless fluffy powder or tiny coated particle.

This powder or coated particle can easily be removed from the cooling tower’s basin by manual means, filtration, or centrifugal separation. The quantity of powder is typically about 15 percent of normal blow-in dirt in a cooling tower.

Particle Separator

Particles can be removed from the bottom of the cooling tower’s basin using a centrifugal separator (Figure 2). Water from the basin is pumped to a centrifugal separator, where it enters the separator tangentially. This gives the water the proper inlet velocity and causes a constant change of direction to generate an initial vortexing action.

Internal tangential slots located on the inner separation barrel causes the water to accelerate further and magnify the vortex strength. Particles in the water are now separated through centrifugal action caused by the vortex. The particles spiral downward along the perimeter of the inner separation barrel and are deposited in a collection chamber below the vortex deflector plate, where they can be automatically purged.

Free of separable particles, the water spirals up the center vortex in the separation barrel and upward to the outlet. A vortex-driven pressure relief line draws fluid from the separator’s solids-collection chamber and returns it to the center of the separation barrel at the vortex deflector plate. This allows even finer solids to be drawn into the solids-collection chamber that would otherwise be re-entrained in the vortex.

Bacterial Control

There are two methods of controlling bacteria or microbial population in cooling tower systems: encapsulation and electroporation.

Normally, bacteria form a biofilm or slime layer on equipment surfaces. The slimy bacterial secretion forms a protective canopy to protect the bacteria beneath it from chemical biocides. It is very slimy to the touch, four times more insulating to heat transfer than mineral scale, and is the primary cause of microbial-influenced corrosion on equipment.

The bacteria that live in a biofilm and adhere to the equipment surfaces are called Sessile bacteria; they represent 99 percent of the total bacteria in a system. However, this slime layer can be eliminated through a process of nutrient limitation.

The suspended particles in the water of a cooling tower incorporate most of the free-floating planktonic bacteria. Normally, since like charges repel one another, the bacteria are repelled by the suspended particles in cooling tower water due to the fact that nearly all tiny particles have similar negative static electrical charges on their surfaces. However, after being activated by the high-frequency electrical pulse field at the water treatment module by the signal generator, the natural electrical static charge on the particle’s surface is removed.

The repulsion to the bacteria is eliminated; therefore, the bacteria are attracted to the powder and become entrapped in it. The powder, in effect, sweeps the water clean of planktonic bacteria and renders them incapable of reproducing. This process is referred to as encapsulation.

The high-frequency, pulsing action of the signal generator also damages the membrane of the planktonic bacteria by creating small pores in their outer membrane. The condition weakens the bacteria and inhibits their capabilities to reproduce. This process is referred to as electroporation. Microbial life has a 24- to 48-hour life span. Any microbe not captured in the forming powder are zapped by the secondary pulse of the signal generator, forcing them to spend their lives repairing cell wall damage rather than reproducing.

All of the living organisms in a cooling tower system depend on one another for their food supply. Thus, when the nutrients from the planktonic bacteria are diluted by both encapsulation and electroporation, the biofilm cannot be sustained and it will disintegrate.

The biofilm will never be created if the cooling tower system is installed using a high-frequency electrical pulse field and creating encapsulation and electroporation processes. The combined effects of encapsulation and electroporation result in exceptionally low total bacterial counts (TBC) in cooling tower water.

Corrosion Control

Most corrosion in cooling tower systems or boilers comes from:

• Chemical additives;

• Softened water;

• Biofilm; and

• Mineral scale.

So, by removing chemicals, avoiding the use of softened water, and using the chemical-free water treatment module and signal generator in cooling tower and boiler water applications, corrosion concerns can be eliminated.

The calcium carbonate that coats the suspended particles is in a state of saturation while it precipitates, and will act as a powerful cathodic corrosion inhibitor. It will greatly slow the corrosion process by blocking the reception of electrons that are thrown off by the corrosion process. With no place for the electrons to go, the corrosion process is physically, very effectively controlled.

Publication date: 09/05/2011
 

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