Without exception, all industrial facilities require the use of water as a coolant, as a means to transfer thermal energy, or perhaps as an ingredient in manufactured products. The extent of water used depends largely on the type of processes and products involved. The quality of incoming, raw water may require treatment or filtration — with higher levels of management or quality control required to meet specific conditions.
For the sake of keeping this article at a basic level, I will not explore the topic as a chemist might. Instead, I will start at a fundamental level to look chiefly at the treatment of boiler water and cooling water.
Industrial process water is used for manufacturing processes such as washing, coating and plating, and rinsing and spraying, and boiler and cooling tower water. There may be several steps involved in the treatment process. To keep this simple, I will focus on:
- Screening and straining.
- Sedimentation and clarification.
- Distribution or release.
Maintaining proper industrial water quality may entail filtration, separation or treatments. Treatment systems are used to introduce and maintain water of optimal quality for many applications. Some of the most common treatments include:
- Raw/incoming water treatment.
- Boiler feedwater treatment. This is chiefly focused on combatting the scaling or mineralization of a heat exchanger.
- Cooling tower water treatment systems. Often, this is intended to reduce total dissolved solids (TDS) to maintain evaporative cooling efficiency and effectiveness.
- Wastewater treatment.
Industrial water conditioning typically involves the adjustment — or preparation of water — as a solution fit to a specific need. This encompasses removing or minimizing the natural or inherent characteristics of water that may be undesirable, such as removing hardness (by softening) to avoid scale, or filtration to minimize particulates. It may also involve adding desirable properties to water such as the addition of phosphate ion as a corrosion inhibitor.
The tools and technologies employed — and the order in which they appear — will vary greatly, largely determined by the contaminants that are involved.
Raw or entry water is water that is introduced into a manufacturing facility, typically sourced from groundwater, wells, lakes and rivers. Raw water may be used for process cooling, rinsing, product formulations or dilution— or, if suitably purified, as a consumable product.
Raw water used for industrial purposes could serve many purposes. For instance, it might be treated and filtered within a cooling tower loop (whether open or closed). Alternatively, it could be used as boiler feedwater, process or production water, or tapped for domestic washing or drinking water within a facility.
Most often, industrial water treatment is tailored to meet specific needs to protect equipment from contaminants — boilers or heat exchangers, for instance — from scaling, fouling, corrosion and other forms of damage. Raw water treatment systems typically remove suspended solids, silica, iron, bacteria and hardness.
Boiler feedwater treatment is used to protect a boiler, pipes, pumps and other components from damage due to contaminants present in the boiler or the makeup water. (Contaminants include dissolved solids, or TDS, suspended solids and organic material such as iron, copper, silica, calcium, magnesium, aluminum, hardness or dissolved gases.) Without proper treatment, boiler feedwater usually will wreak havoc with equipment and piping due to scaling. This can interfere with heat transfer or pump/valve operation. Inadequate boiler feedwater treatment also can contribute to corrosion or fouling of the boiler or other equipment. When any of these situations occur, it can result in costly plant downtime, expensive maintenance charges, loss of operational or energy efficiency, or even equipment failure.
For these reasons, it is important to maintain consistent boiler feedwater quality. Treatment and filtration will remove impurities before the water (or the impurities) enter the boiler and help control the acidity and conductivity of the water. While treatment methods vary, systems typically consist of primary treatment or other aspects, depending on boiler pressure, steam use and chemistry of the boiler feed and makeup water.
A boiler feedwater treatment system usually incorporates the following:
- Makeup water intake.
- Reverse osmosis (RO).
- Primary ion exchange (IX).
- Deaeration or degasification.
Makeup Water Intake. Boilers lose water to steam consumption, loss of condensate return and leakage. Replacement or makeup is drawn from treated city supplies or raw water treatment systems.
Filtration. Typically, water is filtered to remove sediment, turbidity and organic material. Membrane filtration units may be the most cost-effective when used for pretreatment.
Softening. Water softening is used to remove hardness due to calcium and magnesium in the water. It is accomplished by a softening resin, typically a strong acidic resin, that allows it to effectively capture and remove hardness ions from the stream.
Reverse Osmosis (RO). RO can be useful for the removal of bacteria, salts, organics, silica and hardness. RO and nanofiltration both employ membrane filtration to capture contaminants. RO systems for industrial purposes typically provide a 65 to 75 percent recovery rate, which is a very efficient use of water. RO results in exceptionally pure water.
Primary Ion Exchange (IX). For large volumes of water or high pressure boilers, deionizers may be used instead of membrane filtration. Ion exchange typically produces water of comparatively higher quality and resistivity and provides better yields.
Deaeration or Degasification. Following all other treatment steps, the makeup water and condensate from the boiler system are combined and degasified for corrosion prevention.
Distribution. Following all treatment steps, boiler feedwater is piped to a boiler, where it is heated to form steam. From this point, boiler condensate then can be combined with treated makeup water, and the cycle begins again.
Cooling Tower Water
Water that flows to and through cooling towers — feedwater, water for circulation within a cooler or blowdown water — requires treatment and filtration. Equipment and piping must be protected against chlorides, hardness, iron, biological materials, silica, sulfates or TDS, among other challenges.
With circulated water — that is, the water that flows between the plant and a cooling tower — facility managers know to keep a watchful eye on TDS levels. At high levels, the challenge of total dissolved solids must be dealt with. Much of the volume of water must be flushed and, as replacement or makeup water comes in, there are then new concerns to keep water in optimal condition. The better the condition of makeup water, the easier it is to maintain optimal water conditions.
Treatment systems should remove harmful impurities in line with manufacturer recommendations for water quality. Typically, cooling tower water treatment systems will include the following:
- Makeup water intake.
- Side-stream filters.
Makeup Water Intake. With most cooling towers — especially those designed to cool through evaporation — water needs to be replaced. Makeup water for a cooling tower may be drawn from a variety of sources. In some cases, source water must also be treated for hardness, silica, iron or pH adjustment.
Filtration. Source water typically is filtered through one or more types of filtration to remove sediment, turbidity or organic material. This can provide a cost-effective method of fouling prevention and help avoid unnecessary maintenance of downstream equipment.
Softening. If the water has high hardness, a softening resin can be used. Contaminants would otherwise cause scale deposits. Depending on feedwater quality, softening can improve the operational efficiency of cooling towers.
Chemicals. Very often, water for cooling towers may require some form of chemical treatment. This may include corrosion inhibitors, algaecides/biocides or scale inhibitors.
Side-Stream Filters. Many cooling towers recirculate water. Side-stream filtration can be helpful to remove contaminants that have entered through atmospheric contamination.
Post-Treatment. If the volume of water usage is a concern, facility managers may opt to treat the blowdown water through RO filtration for reuse. Other post-treatment systems or methods also may be helpful before discharge.
Water used within an industrial plant is eventually lost due to evaporation, leakage, consumption (if it is an ingredient within a product) or discharge as an effluent that can either be reused or safely carried back into the environment or a treatment facility.
Commonly, the need to avoid harming the environment is paramount. The relative complexity of a wastewater treatment will depend chiefly upon the compliance regulations impacting a plant.
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