Cooling Tower Blowdown Recycling

SAVING WATER THROUGH BLOWDOWN WATER REUSE

 

Cooling towers are open recirculating system designed to reject the heat removed from any commercial or industrial process by means of water evaporation. It is very likely that if you ahve cooling towers installed they will account for a significant proportion, potentially even the absolute majority, of your facilities water consumption.

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During normal operation water evaporates in the cooling tower, this is fundamental in how cooling towers reject heat from your facility, as water evaporates the entrained dissolved ions (Calcium, Magnesium, Silica, etc) remain in the recirculating water stream. As the evaporation continues, the concentration of dissolved ions increases and if this situation continues unaddressed, the solubility limit is reached and problematic scale formation becomes likely.

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The concentration of dissolved ions is reduced by discharging or ‘bleeding’ a portion of the recirculating water to the drain and adding fresh make-up water to replace it. To keep the water balance, the ‘bleed’ (or blowdown) plus the evaporated water must be replaced by make-up water. The cooling tower blowdown stream can represent a significant portion of the total wastewater and recycling this ‘waste’ water can provide significant water savings.

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REVERSE OSMOSIS FOR COOLING TOWER BLOWDOWN TREATMENT AND REUSE

Management of the cooling towers blowdown stream is one of the key activities within the operation and maintenance tasks.

The two main options for the blowdown disposal are:

• Discharge to sewage

• Treatment and reuse

Installing a Reverse Osmosis treatment on the cooling tower blowdown is an option to reduce the facility’s water needs. Reverse Osmosis membranes are used to separate the dissolved ions from the blowdown stream resulting in a high-quality water output that can be reused as make-up water or for the same cooling tower or as a high quality water feed for any other process.

Depending on the blowdown quality, a number of pre-treatment options may be needed to make it suitable for the RO process: filtration, PH adjustment by acid injection and/or softening.

The main benefits of applying a reverse osmosis desalination treatment to the cooling tower blowdown are:

• Lower make-up water demand

• Easier regulation compliance

• Higher number of concentration cycles

• Reduction in chemical treatment

• Consistent water quality

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 OTHER OPPORTUNITIES TO REDUCE COOLING TOWER WATER DEMAND

When Calcium or Magnesium Carbonates and Sulphates are the main factor limiting the cycles of cooling tower water, softening the make-up water can allow the increase of recirculation cycles and reduce the blowdown and with it, the facility’s overall water consumption.

Side-stream filtration systems can improve the quality of the recirculating water removing silt and suspended solids.

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COOLING TOWER WATER REUSE TO REDUCE OPERATIONAL COSTS AND ENVIRONMENTAL IMPACTS

Water and wastewater reuse has become a growing trend due to higher water demand, constant water scarcity and more stringent regulations.

Most cooling towers use tap water as main make-up water supply, what adds pressure to the utility demand. Instead of discharging the blowdown and replacing it with fresh water, increasingly facilities are relying on reusing the cooling tower blowdown to reduce their operational costs and environmental impacts.

By removing a high portion of the total dissolved solids in the blowdown, reverse osmosis simplifies the reuse of the blowdown, allows higher concentration cycles and ultimately reduces frequency of blowdown and fresh make-up water required for the cooling tower operation.

 

IMPLEMENTATION

There are a number of factors in determining if blowdown recycling is appropriate for your facility, however the benefits are such that this is certainly worth exploring. It is recommended that you consult with your cooling tower / water treatment service provider for an initial discussion, alternatively commissioning a feasibility study with an appropriate mechanical engineering consultancy would be a prudent first step.

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