Reducing Environmental Effects of Cooling Towers
NOVEMBER 2014: The implementation of strict environmental regulations worldwide calls for mine operators and managers to take immediate action to reduce the environmental effects of their operations. Cooling towers, a crucial component of the mining process, have naturally come under scrutiny in recent years and it is therefore vital that cooling towers run at optimum efficiency to keep the planet’s water and air clean.
The most common type of industrial cooling tower used in the mining industry is an evaporative cooling tower, which works by dissipating unwanted heat to the atmosphere through water evaporation. This type of water tower emits large quantities of vapour and water droplets of varying sizes (known as drift) into the atmosphere. The drift contains the same chemicals and micro-organisms contained in the cooling tower. These chemicals and micro-organisms carried in the droplets have a detrimental impact on the environment and become carriers of deadly pathogens such as Legionella pneumophila – the bacteria that causes Legionnaires Disease.
Key to preventing the release of hazardous droplets into the atmosphere is to install efficient drift eliminators inside the cooling tower, according to Roger Rusch, MD of Industrial Water Cooling (IWC).
“These baffle-like devices are designed to remove water droplets from the cooling tower’s air stream by changing their direction. This is achieved by making the droplets lose velocity at impact on the blade walls of the drift eliminator, thus causing them to fall back into the tower. This process reduces the amount of potentially hazardous material escaping with the exhaust air,” says Mr Rusch.
The build-up of hazardous chemicals and growth of microbes can be attributed to the collection of suspended solids in the cooling tower’s process water.
In cooling towers that contain packing (used to form a thin liquid film that increases the surface area of the water/air interface for more efficient heat transfer), the suspended solids can block passages in the packing, thus reducing the performance of the cooling tower by decreasing the surface area for heat transfer and creating a more conducive environment for micro-bacterial growth.
To prevent clogging of the cooling tower packing and reduce the potential for this in other process equipment it is crucial to keep the cooling tower’s process water clean at all times. This is achieved by installing the right water filtration system, which will counter the issues caused by the collection of suspended solids, including corrosion and the growth of micro-bacteria.
Full flow and side stream filters are two of the most common filtration systems used in cooling towers. In a full flow system, the filter is installed before the cooling tower, on the discharge side of the pump, and continuously filters all of the recirculating water.
Side stream sand filters work by directing water through a bed of graded filter media, usually made up of compounds such as silica, anthracite or garnet. As the water flows through the bed of sand media, suspended solids and other particles are captured within the upper layer of media. The water moves downward, passing into a drain at the bottom of the filter tank and is discharged from the tower through an outlet pipe.
Using a filtration system ensures that process-water remains clean reducing the need for water treatment chemicals that can have a detrimental impact on the environment. We find our robust range of conventional dual, multi-media and SATI filters covers the entire field of normal filtration requirements from 5000µ(micron) down to 1µ.” says Mr Rusch.
SATI’s extensive product range includes manual, semi-automatic, self-cleaning screen, pleated cartridges and membrane filters. All SATI Filters are constructed with a stainless steel body making them more resistant to corrosion and well suited for harsh operating environments.
The use of non-corrosive materials in cooling tower design is also an important step to the prevention of equipment decay and further contamination of process water.
Says Mr Rusch, “We design and manufacture cooling towers and cooling tower components with non-corroding materials such as GRP; and stainless steels; that are capable of withstanding the extreme temperatures and aggressive chemical processes of mining. Extended longevity and better performance of process equipment as well as timely maintenance of cooling towers are key factors in ensuring the prevention of pollution and environmental hazards.”
IWC, originally founded in 1986 as Industrial Water Cooling, specialises in evaporative water cooling and GRP solutions for numerous applications. IWC are the leaders in industrial cooling tower systems in Africa, offering fully integrated solutions, from industrial cooling towers to GRP. For nearly two decades IWC have successfully undertaken more than 80% of all natural draft refurbishment work in southern Africa. Clients include heavyweights such as Eskom, Sasol, ArcelorMittal and Foskor. Some industries in which the company is involved with are:
• Power Generation
• Steel & Aluminium
• Food & Beverages
• Air-conditioning, Refrigeration and many other applications
For many years IWC has been a member of the CTI, Cooling Technology Institute, based in the USA. This association has as its member’s consultants, designers, constructors as well as end users of cooling towers. With years of expertise and practical knowledge, IWC offers bespoke PHE maintenance solution at cost-effective and competitive pricing.
Due to IWC’s extensive experience in the refurbishment of cooling towers it has undertaken in excess of 80% of the Natural Draught refurbishment work conducted in South Africa.
IWC has completed the on-line refurbishment of a Natural Draught Cooling Tower in Australia and also in South Africa & Zimbabwe. Contact IWC on +27 (0) 11 466 0699