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Proper process monitoring allows a plant to run with minimal operator intervention therefore increasing the cost savings of a typical water purification system. Contributed by Burkert

Proper Instrumentation Monitoring Increases Process Efficiency And Membrane Life In Reverse Osmosis Processes

Scaling, fouling and oxidation are the natural enemies of reverse osmosis (RO) Nano-filtration (NF) systems in water processing units—RO and NF are used in many areas, from drinking water, treatment to desalination of seawater, waste-water treatment all the way to semiconductor, food and pharmaceutical industry. 

Proper process monitoring and control of critical parameters such as pH, ORP, conductivity, flow, temperature and differential pressure can provide advanced warning and protection of a scaling, fouling or chemically attacked RO element. 

If these early warnings are ignored, the membrane may be damaged beyond the point that chemical cleaning can restore the system back to its original operating efficiency.

With the latest range of multifunctional analytical instruments and broad range of switches, transmitters and valves, Bürkert Fluid Control Systems provides intelligent technology that protects membranes, enhances process efficiency, and lowers operating and chemical costs. 

Proper process monitoring also allows the plant to run with minimal operator intervention therefore increasing the cost savings of a typical water purification system.

In the wastewater, desalination, semiconductor, pharmaceutical and biotechnology industry in particular, water quality cannot be compromised. The sustained success of the final product requires consistent process measurement precision.

Of paramount interest in (RO) is the total cost for the complete product cycle, as well as possible strategies to guarantee seamless quality control. This requires integrated solutions like those provided by Bürkert Fluid Control Systems. 

They provide component level products such as pneumatic or solenoid isolation valves, flow measurement devices, conductivity, pH and ORP  transmitters and controllers and implementation of complete cost-efficient control system solutions.

 

Key Elements For Quality And Efficiency

Proper Instrumentation Monitoring Increases Process Efficiency And Membrane Life In Reverse Osmosis Processes

To produce high-purity water for food, pharmaceutical or laboratory purposes, the fluid has to undergo a complicated purification process. 

Pre-treatment processes are essential to ensure all oxidizing agents, organic or inorganic fouling contaminants and scale compounds are eliminated or at least minimised in order to increase the systems total efficiency and lower overall operating costs. 

Preventing RO/NF excessive buildup of these contaminants can be accomplished with proper instrumentation and control processes set in place.

  1. ORP

It is critical to ensure all chlorine or other oxidizing chemicals are removed prior to the feed point of a thin film composite reverse osmosis plant. If left unchecked, these chemicals could physically attack the polyamide membrane and result in significantly lower water quality due to the influx of dissolved salt. This type of damage is non repairable and could result in high replacement costs. 

  1. pH

The perfect pH for RO membranes lay within a slightly acidic environment between five and six. This pH prevents the formation of carbonates and for some cellulose acetate membranes, hydrolysis effects. A deviation from set values automatically triggers a digital dosing pump that adds acid to the RO feed water. This prevents the formation and precipitation of calcium carbonate crystals on an RO membrane which can result in significantly reduced recovery as well as lower water quality.

  1. Conductivity

Conductivity of feed water is one of the key factors for plant recovery rate or flux of the membrane used in reverse osmosis systems. Osmotic pressure increases with conductivity and reduces the efficiency of a system at the same given pressure and temperature. It is important to be able to identify changes in product water production due to feed conductivity fluctuations. 

  1. Temperature

Membrane flux or the amount of water that permeates through an RO membrane is also directly influenced by temperature. The higher the temperature, the higher the flux rate at a given conductivity and pressure. The converse is also true. 

  1. Pressure

RO performance directly depends on feed pressure. Comparative measurements and trending of feed, permeate, concentrate and inter-stage pressures ensures that the system is working at full capacity. Monitoring pressure differentials also helps the operator identify potential first stage fouling or second stage scaling problems. 

  1. Flow Rate

Measured by either a magnetic or paddle flow meter, the percent recovery of the RO system is also a key parameter in determining system health. % Recovery is determined by calculating the percent of the total feed flow that becomes product water or permeate. An increase or decrease of this value at the same given conductivity, temperature and pressure, could be an early indicator of a chemically attacked, scaling or fouling membrane.

 

Cost Efficient Control System

Proper Instrumentation Monitoring Increases Process Efficiency And Membrane Life In Reverse Osmosis Processes

Individual measurements alone will not increase the cost efficiency of the process, even though the latest two-in-one devices like the pH/ORP-transmitters/controllers create synergy on the measurement side. 

Only an efficient process control system that groups and regulates all parameters such as flow rate, temperature, pH/ORP, conductivity and pressure can produce real advantages in performance and efficiency.

 

Multifunctional Control System

Proper Instrumentation Monitoring Increases Process Efficiency And Membrane Life In Reverse Osmosis Processes

A multifunctional control system, like Bürkert’s multi-parameter controller multiCELL 8619, automates the control of process variables in water treatment systems. 

In some cases the controller was able to reduce control and measuring instrumentation costs to almost half. Simple monitoring and control functions, as well as the gathering of data, are integrated in a compact and easily configurable control unit with a display.

Sophisticated electronics and state of the art control algorithms ensure that optimum process control is maintained at all times with minimal operator intervention and achieving highest quality. 

Thanks to full support of the Modbus TCP, PROFINET (Conformance Class B) or EtherNet/IP, the 8619 can be integrated into most Industrial Ethernet environments. 

Therefore all important process values like measurement data, process diagnostics or device status can be easily integrated into the automation system.

An example of % recovery is the relationship between total feed flow and product or permeate flow. A typical brackish water system could operate at 75 percent-85 percent. 

If this value decreases during the course of the process, the control unit monitors and data logs every single parameter that is necessary for fault analysis. 

The initial focus is on pH, then on conductivity, temperature and pressure. Typically, if all parameters are within the control range, but performance of the membranes are still falling short of the nominal value, the issue can be narrowed to a scaling or fouling event. 

This can also be quickly differentiated by appropriate monitoring points. If a higher pressure drop occurs at the first stage, the reason is most often due to colloidal or bio-fouling. A pressure drop increase at the second stage generally indicates an elevated mineral level or scaling occurrence. 

To maximise cost efficiency, a self-contained multifunctional unit can be used to track and log multiple process points simultaneously.

 

Flexible And Scalable Membrane Integrity Test System

To support high productivity of RO and NF systems, Bürkert Fluid Control Systems has developed a flexible and scalable membrane integrity test system. 

Each pressure vessel is connected via tubing to the system. Individual valves control which pressure vessel is being sampled. This automates the sampling of water from each pressure vessel and allows conductivity to be measured and logged quickly & safely. 

Other parameters such as turbidity, pH value, sulphate and chlorine content can be added if required. No more climbing up to each pressure vessel to take manual samples, no more manual data logging. 

If pre-set limit values are exceeded, an alarm can be triggered immediately. More frequent sampling is then triggered for the affected vessel. 

As a result, operators can keep a constant eye on multiple distributed systems easily & safely. Downtime is reduced, while performance is increased and the permeate quality maintained. 

Trend Analysis Enables Preventive Maintenance

The system uses trend analysis to enable early detection of membrane breakage. Trend reports can be separately created for every pressure vessel and therefore provides information about the membrane integrity of the individual pressure vessels. 

Problems can then be quickly localised to avoid production interruptions. Incorporation into the plant-specific communications system, the Profinet/Profibus, Ethernet/IP, Modbus TCP/IP, EtherCAT, CC-Link IE, CANopen interfaces are available for IIOT/ Industry 4.0 integration for remote access of data from desktop to mobility devices.

The permeate monitoring system consists of type 0127 solenoid valve, 2/2-way or 3/2-way valve which is ideal for use in lab, medical and analysis technology. 

The rocker technology that actuates the separating membrane between the drive and the fluid has set standards. 

The valve, which features protection type IP54 as well as high resistance to chemicals, controls even minimal volumes with very high precision. The temperature generated by the coil is minimal, as is the internal volume. The valves feature excellent flushability, with practically no dead zone.

Conclusion

Depending on the complexity of the RO/NF process, state-of-the-art measurement and control systems ranging from relatively simple transmitters/controllers to powerful multifunctional control boards, enhance process efficiency and increase the durability of process technology. They also reduce the costs for control and measuring instruments.

 

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