THE DEFINITIVE GUIDE TO INDUSTRIAL WATER TREATMENT

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To achieve and meet the industrial water treatment standards it is necessary to understand the application that the water will utilized for and what type of contaminants if left untreated will be harmful for the end use.  If the water will be utilized for multiple applications, then it is important to select the most stringent application and its requirements to be sure that the design and performance of the water treatment system meets the standard.  The process design should be engineered to meet the more stringent requirements.  A typical example of water diversification needs is steam.  Steam can be needed to provide plant heat for freeze and flow protection and is needed or incorporated into the actual process to produce a product.  Typically, membrane filtration and decarbonation followed by Ion exchange, and or demineralizers are utilized to achieve these results.

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WHAT IS INDUSTRIAL WATER TREATMENT?

Industry factory in kawasaki at nightWikipedia as, “any water used to optimize most-water based industrial processes, such as heating, cooling, processing, cleaning, and rinsing to that operational costs are reduced”.  We who are involved within the industry of treatment industrial water and removing dissolved mineral salts, hydrogen sulfide gas (H2S)carbon dioxide gas (CO2), realize how important the proper treatment of water becomes in an industrial applications for use in boiler feed systems and steam generation. 

In order to comply with the tight operational standards and to meet the industrial process requirements water professionals must design and manufacture industrial water treatment equipment capable of performing functions such as decarbonation to remove CO2 in an effort to prevent carbonic acid formation. Decarbonation towers and dearation towers strip CO2 (carbon dioxide) and H2S (hydrogen sulfide) dissolved gases to prevent harmful scaling and corrosion and to lower operational costs. 

The main objective of industrial water treatment

is to prevent corrosion, scaling, biological growth and to ensure that water disposal standards are met.  Without the removal of the harmful mineral salts, and corrosive gases the industrial process equipment infrastructure such as the piping, cooling towers, and boilers systems would all suffer from the potential of corrosion, scaling and ultimate system failure.  A catastrophic system failure can occur when industrial water treatment processes become out of balance and critical components are exposed to harmful corrosive of scaling conditions.  Critical functions such as steam production are often shut down due to scaling or corrosion that attacks boiler tube efficiency. 

Reverse Osmosis

Typically an industrial water treatment system utilize several types of processes in series or in parallel to meet the specified water quality for the industrial process, steam generation, or incorporation into a food or beverage. There are several types of process commonly utilized within the industrial water treatment industry.  Membrane filtration (reverse osmosis), (water filtering) will often be followed by dearation, degasification, or decarbonation followed by additional ion exchange treatment and for disinfection the process of chemical treatment,  ozonation, and or U.V. ultraviolet  are all utilized for disinfection.

Membrane filtration

or more commonly known as “reverse osmosis” is a process where water is forced through a semipermeable membrane to remove molecules, ions, and larger particles.  The membrane is encapsulated within a vessel or tube and an applied pressure is used to overcome the osmotic pressure of the water.  The pressure is generated by a high pressure pump and the pump pressure may vary depending on the type of membrane, condition of the raw water, and the final water quality needed.  The treated water is referred to as “permeate” and the reject water is referred to as “concentrate”.  The solids comprised of molecules, ions, or even bacteria remain on the outside of the membrane and are rejected through the end of the tube.  Water with particulate or non-dissolved solids are measured by conductivity and is often reported as TSS (total suspended solids).

Dearation is a process

where steam and water are introduced into a dearator “packed column tower” to force a “degasification” process of gases to occur.  Steam is utilized to heat water to near saturation point while maintaining a lower pressure vent.  This is achieved by spraying water into a vertical packed dearator tower equipment with a distribution system which can be a weir tray or header lateral and multiple layers of trays or random packed media. Steam is introduced typically at the bottom of the tower and is forced to impact with the falling water.  The heated steam from the boiler feed water system raises the water temperature to saturation level and the dissolved gases are released from the water.  Deaerators are utilized in industrial applications to remove oxygen primarily but can also remove CO2 (carbon dioxide gases). 

Decarbonation and Degasification towers

are also vertical towers and utilize a distribution system and media bed which can be either PVC tray type or random packed media supported by a false bottom.  A decarbonation tower and degasification tower both utilize a blower to create a cross current airflow within the tower as it impacts the inlet feed water.  Water is introduced at the top of the tower and by gravity it travels down and across the media bed as the cross current air flow travels upwards and is exhausted at the top of the tower.  Decarbonators and degasifiers can be either induced draft or a forced draft design. 

The efficiency of a decarbonator and degasifier to remove dissolved gases such as carbon dioxide (CO2) or hydrogen sulfide (H2S) is far greater than that of a deaerator as it does not require the introduction of steam.  The decarbonator and degasifier efficiencies increase with the rise of water temperature, proper pH adjustment, media type selection, and air flow volume.  The removal of the dissolved gases from the decarbonator and degasifier is based upon the chemistry law and is referred to as “Henry’s Law.  Henry's law states that the amount of dissolved gas is proportional to its partial pressure in the gas phase.  The proportionality factor is referred to as the “Henry’s law constant”.

Henry's_Law

When water passes through a decarbonator or degasification tower the gases are released.  The release of gases is possible from the reshaping of the water, exposing the gas molecules, and cross current air flow that creates the disproportional pressure imbalance within the tower.  There are two types of processes that can reshape water within a packed tower. The first process is called “controlled film” and this defines spreading the water thinly over a surface allowing the molecules of dissolved gases to reach the surface of the water and be exposed to the cross current air flow.  The second process is called “impingement” and with impingement water falls from one point to another where the water impacts and is “fractured” causing molecules of dissolved gases to be exposed to the surface of the water and be in contact with the cross current air flow.  In both cases the “steady state” of the water is altered by the cross current air flow and the reshaping of the water to expose molecules of gas.  This creates the disproportional relationship of pressure and allows the gases to be stripped and ejected with the exhaust air stream.  existing water tension biding the dissolved gas molecules.  Different types of media beds for decarbonation and degasification towers have different removal efficiencies and are calculated by defining the NTU (number of turn units) or HTU (height of the turn unit) values.  Media with higher NTU and HTU values typically yield higher removal efficiencies.     

Ion exchange treatment

within the industrial water treatment market plays a significant role in the protection of critical components such as boiler feed systems and cooling towers.  Without ion exchange the ability to generate steam at a reliable and cost effective manner in many locations would be difficult if not impossible.  Ions are charge molecules or atoms and when an ionic substance is dissolved in water the molecules dissociate into cations.   “Cations” are positively charged particles.  Negatively charged particles are referred to as “anions”.  Ion exchange resins work by attracting other molecules or atoms based upon their electrical charge and replacing them within the water process leaving the removed molecule attached now to the resin within the ion exchange system.  Over time the ion exchange system becomes saturated and it must be back washed, regenerated and recharged.  This is typically done with a backwash system and regenerate solution located near the ionic exchange process equipment.

Cationic exchangers are normally classified as either strong (SAC) or weak (WAC) acid systems depending on the type of resin the unit is charged with.  Both strong and weak acid resins are utilized in the demineralization process at industrial water treatment locations.  Strong acid cations are utilized for water softening and weak acid cation systems are used for dealkalization applications.  Contaminants typically removed by cation resins include:

Calcium (Ca2+), Chromium (Cr3+ and Cr6+), Iron (Fe3+), Magnesium (Mg2+), Manganese (Mn2+), Radium (Ra2+), Sodium (Na+), and  Strontium (Sr2+).

Anionic exchangers are normally classified as either strong (SBA) or weak (WBA) base anion systems depending on the type of resin the unit is charged with.  Strong base anion resins are utilized in the demineralization process at industrial water treatment locations while weak base anion systems are used for acid absorption.  Contaminants typically removed by anion resins include:

Arsenic, Carbonates (CO3), Chlorides (Cl-), Cyanide (CN-), Fluoride, Nitrates (NO3), Perchlorate (ClO4-), Perfluoro octane sulfonate anion (PFOS), Perfluorooctanoic acid (PFOA), Silica (SiO2), Sulfates (SO4), and Uranium.

Preventive Maintenance

Industrial water disinfection is required to prevent the formation or contamination of bacteria into the water processes.  Bacteria can damage both equipment and products when it flourishes within an industrial water process causing harmful and even dangerous results when not properly prevented.   Water processes involving the pharmaceutical and food and beverage industry are especially careful when it comes to the treatment and disinfection of water.  Chemicals like chlorine and ozonation are utilized as a means to kill and prevent the formation of bacteria.  The disadvantage to utilizing chemicals is the potential to alter the water chemistry further or impact the taste of the water. As an alternative the use of ultraviolet light for disinfection has become a very common process over the last 20 years.  

The need to maintain tight water quality standards

Ultra Violet Light water treatment

creates the requirement to maintain good service and cleaning events of the water treatment systems involved in the industrial water processes.  Decarbonation and degasification towers should be inspected and cleaned on a regular cycle and the media beds cleaned and or replaced to prevent poor performance and system failure.  Without proper maintenance these towers cannot efficiently remove hydrogen sulfide gases, carbon dioxide gases, and the removal or inducement of oxygen gases. Maintenance schedules control operational costs and these costs will rise and when left unattended and can push an industrial operational budget into the red.

Industrial water treatment is also utilized to purify the water for other types of manufacturing where the water will either come in direct contact with the manufactured products like in the semi-conductor market where the water is used to clean the surface during manufacturing.  The removal of both harmful solids, minerals, iron and mineral salts along with the prevention of bacteria growth is a required standard.  Industrial water can also be directly utilized where it is incorporated into the final end products such as the pharmaceutical or the food and beverage industry.

The disposal of industrial water

after it has performed its primary function is as critical to meet the stringent environmental requirements.   The processes for the treatment of the waste stream of an industrial application often times mimics the in fluent industrial water treatment process requirements. This is no surprise because in the USA and other countries the regulatory agencies have adopted “drinking water standards” for most reuse or waste water disposal requirements. Water is treated by means of filtration, degasification, chemical injection for pH adjustment, and membrane filtration.  Reverse osmosis is commonly utilized to return water back into a “reuse” or safe to discharge category.

In addition to the treatment of industrial water often times the air stream that is generated during the process must also be treated because it can cause both a human concern for workers or create an corrosive condition in the air which can also damage the surface of surrounding equipment or instrumentation.  The removal of hydrogen sulfide gases are very corrosive and often must be treated with an industrial chemical scrubber or a biological scrubber.  When treating industrial water in the semiconductor market or plating industry corrosive gases must be neutralized.  A chemical scrubber utilizes a packed tower system with a distribution system located at the top of the tower.  The scrubber can be a single or double pass tower and will be equipped with random packed media.  The type of scrubbing solution depends upon the type of gas that is being neutralized.  For hydrogen sulfide scrubbers the use of chlorine and caustic are often deployed as effective methods to treat the hydrogen sulfide gas. 

A more recent alternative that offers lower operating cost and is a more simplistic piece of equipment to operate and maintain is a biological scrubber.  A biological odor control scrubber utilizes a packed tower design like a chemical scrubber but instead of a recirculating reagent  to oxidize of absorb the corrosive hydrogen sulfide gas it utilizes a colony of bacteria that have been specifically cultured to digest the elements within the gas stream.  The re-circulation process is utilized to add constant moisture to the media bed and to inject nutrients when needed.  The use of a biological odor control scrubber over a chemical odor control or gas scrubber depends on the type of air stream, the concentration, and any fluctuation within the load rates.  Biological scrubbers to not adjust to high and low concentrations that change quickly unlike a chemical scrubber that can be charged with sufficient oxidation chemicals to instantly react to varying load rates.

Conclusion

whether the industrial water process is being used to convert to steam, clean, rinse, treat, or be incorporated into a final product the need for proper industrial water treatment and off gas treatment remains the same and design professionals have an wide selection of industrial water treatment equipment and systems produced by manufacturers like DeLoach Industries Inc., to assist them in developing the highest quality systems for each application.

 

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