Real-Time Sensing and Process Control:

Introducing ScaleSense for Ca2+, Ba2+, SO42-, and SiO2

Key Takeaways

  • Real-time measurement provides prompt feedback for controls. A real-time sensor can help to optimize your process, reduce risk, and minimize operational and maintenance demand.
  • Many real-time measurement methods struggle in challenging environments, with waters that have high total dissolved solids (TDS), or waters that are otherwise highly impaired.
  • Real-time measurement and controls on sulfates, calcium, barium, or silica can be useful in a host of applications explored in this blog—from mine water treatment, to boosting reverse osmosis (RO) water production while generating less brine.
  • Saltworks has developed a new real-time sensor—that is simple and robust—to operate in the high-TDS range.

Real-Time Measurement & Controls

If “that which is measured, improves”, then that which is measured in real-time can also be improved in real-time. Obtaining and analyzing data faster—and adjusting a process accordingly—yields substantial efficiency gains. Furthermore, data acquired continuously does not just present one ‘snapshot-in-time’ but can show trends and variations. This type of continuous data facilitates forecasting, allowing anticipatory actions to be taken. Modern operational technologies such as real-time sensors allow process control with unprecedented agility.

 

While some wastewater treatment or discharge processes use real-time controls, there remain many flows that are difficult or even impossible to measure continuously. Developing a sensor for high-TDS flows that is pH-resistant, easy to-clean, and exhibits high-throughput has proven challenging. In this blog we discuss real-time measurement, briefly review some existing sensor technologies, introduce a new ion selective sensor product (ScaleSense), and then explore some case studies in which a new sensor can be of great benefit.

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Figure 1. Our new ScaleSense real-time sensor.
Figure 2. ScaleSense can be used to measure Ca2+, Ba2+, SO42-, and SiO2.

Sensors in Impaired Water

There are many sensing and detection methods—with different advantages and disadvantages—used for measuring ions and other chemical species in industrial wastewaters. Among them are chemical titration and colorimetry (spectrophotometry operating within the visible range). Titration is usually a slow process, requiring a lot of skilled operator time. Colorimetry can be performed manually by an operator, or automatically using an appropriate system. However, signals in colorimetry become saturated for high-TDS (>50,000 mg/L) wastewaters, leading to poor performance for highly impaired water. Although this can be mitigated by dilution with deionised or distilled water, this has disadvantages, such as decreased accuracy. The table below shows a comparison of titration, colorimetry, and our new ScaleSense product.

Parameter Titration Manual Colorimetric Auto-Colorimetric ScaleSense
Real-Time Digital Feedback Offline Offline Real-Time Real-Time
Resolution/Uncertainty (±%) ~0.1–1 0.1–1 2 ~2–5%*
Temperature (°C) -5–100 0–40 5–50 -5–80
Testing Volume (mL) ~1–100 ~2–50 Continuous Continuous
Testing Rate (mL/min) Static Static 100–500 Up to 300
Analysis Cycle Time (mins) ~5 ~2–100 ~7 ~5
High TDS Operation Not Accurate

ScaleSense: A New Real-Time Sensor

ScaleSense is a novel, specific real-time sensor for saline waters. It can measure calcium (Ca2+), barium (Ba2+), and sulfate (SO42-) ions and silica (SiO2). ScaleSense was developed to operate on the most challenging waters, especially those in which other real-time sensors do not function effectively. It functions accurately and precisely, even at extremely high-TDS. It is simple, robust, and easy-to-clean. ScaleSense is also corrosion-resistant and operates well over broad temperature (5–80°C) and pH (0–14) ranges. ScaleSense response is sharply defined and accurate, providing fast and continuous feedback for a control that can work well, even with a fluctuating wastewater chemistry.

sulfate-sensor-response 2
Figure 3. ScaleSense response to sulfate injection.

Application Case 1: RO Reliability and Recovery Maximisation

Reverse osmosis (RO) is an essential and widespread water treatment technology. Recently, ultra-high-pressure RO has been developed to achieve ultra-high recoveries. When high recoveries are sought in RO systems, they are usually bottlenecked by scale. For the safe operation of RO systems, the brine concentration should not exceed that which produces scaling with compounds such as CaSO4—they damage the membrane.

 

As inlet chemistry changes, an ion-specific sensor in communication with the RO system can adjust brine volume and recovery on the fly. If, for example, a chemical softening system was employed, an ion specific sensor can optimize chemical consumption, while protecting the membranes. ScaleSense can behave as a “virtual anti-scalant”, providing dynamic recovery control, to get the best out of RO and softening processes while protecting membranes.

diagram
Figure 4. ScaleSense maximising recovery and protecting an RO membrane system from scaling.

Application Case 2: Mining and Industrial Wastewaters

Some industrial or mining facilities may need to reduce sulfates in discharges. Continuous monitoring enables better decisions with data. If treatment is required, hydraulic capacity can be minimized and cost saved by treating and blending, in an automated fashion to always meet the discharge limit.  For example, in a sulfate process which uses nanofiltration, a sensor could maximise recovery; or alternatively in a barium precipitation system the chemical costs can be minimized by knowing sulfate concentrations and dosing accordingly.

Figure 5. ScaleSense optimizing sulfate discharge in industrial and mining processes.

Application Case 3: Cooling Tower Blowdown Reduction

The vast majority of freshwater used in all of industry passes through cooling towers, which are widely used in processes such as thermoelectric power generation (coal, oil, natural gas, nuclear etc.). One of the greatest opportunities to reduce freshwater consumption is by optimizing cooling tower function.

 

In cooling tower operation, hot water is sprayed in, some of which evaporates. The cooler water is collected at the bottom. Over time, this can become high in total dissolved solids (TDS). To mitigate this effect, high-TDS “blow-down” water is removed, while “make-up” or low-TDS water is injected. Some cooling towers are scale-limited and require the use of anti-scalant chemical consumables, often in excess quantities to ensure that scale does not form.

 

The image below shows how a real-time sensor can help to improve cooling tower function. An accurate measurement of scaling ions means that the real scaling risk—rather than assumed risk—can be known. Blowdown cycles can be optimized, enabling freshwater savings and less blowdown. Superfluous freshwater consumption and anti-scalant treatment can therefore be safely reduced on scale-limited towers.

Figure 6. ScaleSense reducing cooling tower blowdown, reducing water consumption.

Application Case 4: Protecting Disposal Wells

Disposal wells are widely used to manage many fluids, by placing them deep underground. A problem which often arises in the disposal well industry is the inadvertent plugging of active wells, which can be caused by the mixing of incompatible wastewaters that produce a solid. Disposal wells may receive wastewaters from different sources. For example, one wastewater might be rich in sulfate ions, while another is rich in barium ions. If allowed to mix or “co-mingle”, the dissolved solids may react to form barium sulfate, a water-insoluble solid which precipitates and risks plugging the well.


Similarly to the above Figure 5, a real-time sensor can protect a disposal well. In the example of a disposal well, a wastewater that is high in one of barium or sulfate can be diverted into a separate stream for management including pre-treatment. The disposal well is therefore protected from inadvertent plugging caused by the co-mingling of different wastewaters.

Application Case 5: Protecting Offshore Oil & Gas Reservoir Assets

During the extraction of oil from offshore reservoirs, the injection of seawater is used to maintain output by preserving pressure. Sometimes the seawater is desalinated, but more often it is treated with nanofiltration. Seawater contains sulfates, which can promote the growth of sulfate-reducing bacteria. This leads to the formation of sulfides such as hydrogen sulfide. The presence of such sulfides causes the oil to become ‘sour’, i.e. the total sulfur level is >0.5%. This sulfur content needs to be removed before the oil can be refined into petrol—which is costly, but necessary to meet regulations. Injecting sulfates can also form scale or plug the reservoir in certain cases. Therefore, it is important to know if sulfates are inadvertently being injected, and quality assure the injection water system.

 

ScaleSense can monitor sulfates, allowing their controlled treatment for reduction before injection, protecting valuable reservoir assets and minimising the need for any subsequent treatment. It’s small footprint makes it a good fit for offshore operation.

Figure 7. Protecting offshore oil & gas assets with ScaleSense.

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