Legionnaires cooling tower its Nomenclature

Another very important reason for using biocides in cooling towers is to prevent the growth of Legionella,including species that cause Legionnaires' disease or Legionnaires' disease, most notably Legionella pneumophila or Mycobacterium avium.Various Legionella bacteria are the cause of Legionnaires' disease in humans and are transmitted by exposure to aerosols inhalation of mist droplets containing the bacteria.Common sources of Legionella include cooling towers used in open recirculating evaporative cooling water systems, domestic hot water systems, fountains and similar propagation devices connected to the public water supply.Natural resources include freshwater ponds and creeks.

French researchers found that Legionella bacteria spread 6 kilometers (3.7 miles) in the air of a large contaminated cooling tower at a petrochemical plant in the French province of Pas-de-Calais.That outbreak killed 21 of 86 people with laboratory-confirmed infection.Drift (or windage) is the term for process water droplets that are allowed to escape in the cooling tower discharge.Drift eliminators are typically used to maintain a drift rate of 0.001–0.005% of the circulating flow rate.Typical drift eliminators provide multiple directional changes in airflow to prevent water droplets from escaping. A well-designed and installed water eliminator can greatly reduce the chance of water loss and exposure to Legionella or water treatment chemicals. Also, check the condition of the eliminator approximately every six months to make sure there are no gaps for dirt to flow freely.

The U.S.Centers for Disease Control and Prevention (CDC) does not recommend routine testing for Legionella pneumophila in healthcare facilities.Regular microbiological surveillance for Legionella remains controversial because its presence is not necessarily evidence of an underlying disease cause.The CDC recommends aggressive disinfection of equipment known to transmit Legionella, but does not recommend routine microbiological testing for the bacteria. However,regular monitoring of drinking water in hospitals may be considered in certain settings where people are at high risk of illness and death from Legionella infection (e.g. hematopoietic stem cell transplantation units or solid organ transplantation units ).Additionally, following an outbreak of Legionnaires' disease, health officials agree that surveillance is necessary to identify the source and assess the efficacy of fungicides or other preventive measures.

Nomenclature:

Windage or Drift Water droplets are carried out of the cooling tower with the exhaust air.The drifting droplets have the same concentration of impurities as the water entering the column.Drift rates are usually reduced through the use of baffle-like devices called drift eliminators through which the air must pass after leaving the fill and injection areas of the tower.Drift can also be reduced by using higher entering cooling tower temperatures.Blow Out Water droplets are blown out of the cooling tower by the wind, usually at the air intake.In the absence of wind, water may also be lost through splashing or fogging.Devices such as windshields, shutters, splash guards and diverters are used to limit these losses.Plume the saturated exhaust stream leaving the cooling tower.The plume is      visible when the water vapor contained in the plume condenses when it comes in contact with cooler ambient air, just as the saturated air in a person's breath atomizes on a cold day.In some cases, cooling tower plumes can pose a fogging or icing hazard to their surroundings.Note that the water that evaporates during cooling is "pure" water, as opposed to drifting droplets or very small proportions of water being blown from the air intake.Draw-off or Blow-down Removal of a portion of the circulating water stream (usually to drain) in order to keep levels of Total Dissolved Solids (TDS) and other impurities acceptably low.The higher TDS concentration in the solution may be due to a more efficient cooling tower.However, the higher the TDS concentration, the greater the risk of scaling, biological growth and corrosion.The blowdown capacity is mainly specified by measuring the conductivity of the circulating water.Chemicals (biocides, sulfuric acid, corrosion inhibitors respectively) prevent biological growth, scaling and corrosion. On the other hand, the only feasible way to reduce the conductivity is to increase the blowdown and then increase the clean make-up water.

• Cooling Tower Zero Blowdown, also known as Cooling Tower Zero Blowdown, is a process that significantly reduces the need to drain water with trapped solids from the system by leaving the water with more solids in solution.

• Makeup Water-Water that must be added to the circulating water system to compensate for water losses such as evaporation, drift losses, blowouts,blowdowns, etc.

• Noise-the sound energy emitted by a cooling tower and heard (recorded) at a given distance and direction.The sound is produced by the impact of falling water, the air movement of the fan, the movement of the fan blades in the structure, the vibration of the structure, and the motor, gearbox or drive belt.

• Method is the temperature difference between the cooling water temperature and the wet bulb temperature (twb) of the incoming air.Since cooling towers are based on the principle of evaporative cooling, the maximum efficiency of a cooling tower depends on the wet bulb temperature of the air. Wet bulb temperature is a temperature measurement that reflects the physical properties of a system of gas and vapor mixtures (usually air and water vapor)

• Range is the temperature difference between the warm water inlet and the cold water outlet.

• Packing: Inside the column, packing is added to increase the contact surface and contact time between air and water to provide better heat transfer.The efficiency of the column depends on the choice and amount of packing.Two types of padding can be used:

• Thin-film fill (diffuses water into a thin film).

• Splash fill (shatters falling water and interrupts its vertical progression).

• Full Flow Filtration-Full Flow Filtration continuously filters particulates from the entire system flow. For example, in a 100 ton system, the flow rate is approximately 300 GPM. A filter will be selected to accommodate the full 300 gpm flow rate.In this case, the filter is usually installed after the cooling tower on the discharge side of the pump.While this is ideal for filtration, it can be cost-prohibitive for higher flow systems.

Sidestream Filtration-While popular and effective, sidestream filtration does not provide complete protection.With sidestream filtration, a portion of the water is continuously filtered.The method works on the principle that continuous particle removal will keep the system clean.Manufacturers typically package sidestream filters on a skid complete with pump and controls.For high flow systems, this method is cost effective.Proper sizing of sidestream filtration systems is critical to achieving satisfactory filtration performance, but there is some debate about how to properly size sidestream systems.Many engineers size systems to continuously filter cooling tower sump water at a rate equal to 10 percent of the total recirculation flow.For example, if the system has a total flow of 1,200 gpm (400 ton system), specify a 120 gpm sidestream system.Concentration cycle the maximum allowable multiplier for the amount of      miscellaneous substances in the circulating water compared to the amount of these substances in the make-up water.

• Treated wood a structural material used in cooling towers that was largely abandoned in the early 2000s.Despite its short life expectancy, it is still used occasionally due to its low initial cost.The lifetime of treated wood varies widely, depending on tower operating conditions, such as frequency of shutdowns, treatment of recirculated water, etc. Under proper working conditions, the estimated life of treated timber structural members is approximately 10 years.

• Leaching-Loss of wood preservation chemicals by the flushing action of water flowing through a timber cooling tower.

• Pultruded Fiberglass -A common structural material for small cooling towers, Fiber Reinforced Plastic (FRP) is known for its high corrosion  resistance.Pultruded FRP is produced by pultrusion technology and has become the most commonly used structural material for small cooling towers.It costs less and requires less maintenance than reinforced concrete, which is still used in large structures.