APPLICATIONS
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The Refex electrode is exceptionally resistant to applications containing poisons, even those with components such as cyanide, ammonia and sulfides. This immunity is achieved because the polymeric reference junction is non-porous and prevents process material from invading and contaminating the electrode internals, causing drift and inevitable failure.
Below are a few examples where REFEX sensors can make a difference
Municipal Waste Water Treatment
Sulfides build up in waste water systems due to the anaerobic (without oxygen) conditions that such plant is operated under.
Portable Water
REFEX Water Treatment pH Systems are designed to give reliable, continuous real time measurement of water quality in water treatment systems.
Oil & Gas Refineries
Traditional pH and ORP sensors with porous/open reference junctions that are used in processes containing aggressive and toxic chemicals often fail because of reference electrode poisoning. Chemicals from within the process diffuse through the built-in porous/open junction(s) necessary for this type of sensor to operate and poison the Ag/AgCl electrode within the reference half cell.
Optimized Coagulation
Deviations from optimum coagulation conditions (i.e. coagulant chemical dosing rates and pH) can seriously affect treatment performance in water treatment plants. Coagulant chemicals are often sensitive to pH and perform best when pH is maintained within a tight range
Often, turbidity and NOM removal performance is best achieved at pH ranges from 5 to 6, while at pH > 6, NOM removal efficiency lessens significantly and requires higher dosage of coagulant. It is clear that rapid and large variation in raw water quality represents major operational challenges to ensure optimal coagulation conditions suitable to the actual raw water quality are maintained.
REFEX solid state reference electrodes provide instantaneous response to pH change. This very important measurement quality is vital where chemical dosing is required to maintain optimal conditions as slow response can lead to both over- and under-dosing of often expensive correction chemicals – increasing costs directly with greater use of correction chemicals and indirectly by lowering coagulation efficiency.
The slow response of conventional electrodes in correction chemical control systems leads to over-shoot of set points (Fig. 1) and therefore greater chemical usage – correction chemicals are needed to correct for the overcorrection!
REFEX reference electrodes provide rapid response because their entire wetted surface is electrochemically active. This helps to prevent pH over-shoot (Fig. 2), resulting in significant chemical savings and improved operational efficiency.
Ultra Pure Water
The REFEX Ultra-Pure Water pH System is designed to give reliable, continuous real time measurement of water quality in water purification and distribution systems.
Designed to be operated as a side steam, the system is supplied complete with a purpose built flowcell assembly that houses the measurement electrodes.
REFEX reference and glass pH separates are provided. The robust reference sensor uses a highly stable non-porous polymeric interface instead of a traditional porous liquid junction as used by all conventional reference electrodes. The non-porous nature of the electrode interface prevents the loss of electrolyte into the flow stream, a serious problem in all conventional probes. The maintenance of the reference cell in this way prevents the rapid degradation of the measurement, greatly reduces the maintenance overhead and no longer requires the frequent replacement of “consumable” probes.
Where needed, an optional Conductivity sensor with low cell constant can be fitted into the measurement loop as an additional parameter.
To complete the package, a multi-parameter analyzer unit is used to give and transmit real time pH, conductivity and temperature information to local SCADA and control systems.
Petroleum Refining – Sour Water Stripper
Used to remove gases such as ammonia and dissolved hydrogen sulfide from sour water, sour water strippers present an extremely challenging pH measurement application. Strippers are operated at about 80°C to facilitate removal of these gases.
Oil Refinery Desalter Wash and Brine Water
The REFEX Ultra-Pure Water pH System is designed to give reliable, continuous real time measurement of water quality in water purification and distribution systems.
REFEX reference and glass pH separates are provided. The robust reference sensor uses a highly stable non-porous polymeric interface instead of a traditional porous liquid junction as used by all conventional reference electrodes. The non-porous nature of the electrode interface prevents the loss of electrolyte into the flow stream, a serious problem in all conventional probes. The maintenance of the reference cell in this way prevents the rapid degradation of the measurement, greatly reduces the maintenance overhead and no longer requires the frequent replacement of “consumable” probes.
Where needed, an optional Conductivity sensor with low cell constant can be fitted into the measurement loop as an additional parameter.
To complete the package, a multi-parameter analyzer unit is used to give and transmit real time pH, conductivity and temperature information to local SCADA and control systems.
Petroleum Refining – Sour Water Oil Refinery Wastewater Treatment
Refinery wastewater contains challenging contaminants that must all be removed before the water is either recycled for reuse in the plant or discharged to the environment. Contaminants include residual hydrocarbons, sulphur and chloride salts from sour crude refining, ammonia, cyanides, hydrofluoric acid, benzene and toluene. To eliminate these contaminants, the wastewater is subjected to a coagulation process where Alum and polymers are added. These create a ”floc’ that captures the contaminants in a sludge that can be dried and disposed of. Accurate pH measurement and control is vital to ensure coagulation and floc is optimal. Refinery wastewater is oily/dirty and can soon destroy typical traditional pH probes, even those labeled and promoted for “severe service” The non-porous nature of REFEX pH probes makes them the best solution for this type of extreme application
Chlor-Alkali – Chlorinated and Waste Brine
Chlorine gas is produced in a membrane cell chlor-alkali process. Saturated brine is introduced into a high voltage electrolysis cell where chloride ions are oxidized to chlorine gas at the anode.
To optimise yield while minimising corrosion damage to the expensive electrolysis membrane cell, brine pH must be carefully controlled between pH 2.00 and pH 4.00 by the addition of HCl.
Depleted brine from the cell is re-saturated with salt in a recirculation system for reuse over and over again. After leaving the electrolysis cell, the pH of the brine is adjusted to between 10 and 12 so that impurities in the brine (such as metals and sulphates) can be removed by precipitation. pH measurement and control by the addition of Hydrochloric Acid (HCl) and Sodium Hydroxide (NaOH) is critical throughout the entire process.
The challenges of reliably measuring pH in brine applications are severe. KCl is typically used in pH probe reference junctions because the equivalent conductance of a Potassium ion (K+) and a Chloride ion (Cl-) are almost the same. The equivalent conductance of a Sodium ion is much less, a Hydronium ion much higher, causing significant asymmetry potentials in the electronic circuit. This leads to measurement error and accelerated KCl diffusion across the electrode junction. Chlorinated brine pH is measured close to the electrolysis cell electrodes where very high electrical currents are present. These currents cause ground loops in the pH measurement circuit, creating offsets and shortening electrode life. In short, pH measurement in the process using traditional electrodes quickly becomes sluggish and inaccurate, causing waste of pH correction chemicals and impacting plant performance and yield.
The solution to these problems is a pH probe using a REFEX solid state non-porous reference interface – an electrochemically active, ionically conductive interface that forms an impenetrable barrier between the process brine and the Ag/AgCl reference electrode in 2.8 mol /l KCl electrolyte. Non-porous REFEX electrodes are immune to KCl loss/diffusion, ground-Loop currents (a liquid Earth should always be used), fouling and poisoning.
REFEX pH and REFEX ORP combined electrodes are the only ones that can withstand all chlor-alkali application challenges. The patented REFEX non-porous reference interface has solved many of the measurement problems of the past.
Biotechnology
Biotechnology processes are carried out in a sterile and highly controlled environment to prevent contamination and loss of material. Loss can be very expensive, with some media costing astronomical amounts of money. To prevent cross contamination between batches, pH probes are often discarded after only being used once. The porous nature of traditional probes makes them impossible to clean completely, hence the disposable approach. REFEX probes can solve this issue as they are intrinsically non-porous and totally cleanable. Furthermore, the reference junction material is resilient to sterilization, with tests proving that REFEX reference probes can be sterilized many, many times without loss of effectiveness or operation.
pH Neutralization in Industrial Waste water
There are many regulatory requirements at both State and Federal level regarding the discharge of wastewater from industrial manufacturing facilities.
Any company that discharges any sort of effluent into sewer systems, lakes, streams or the ocean is required to neutralize this effluent before discharge. Non-compliance can result, at a minimum in financial penalties and may include other consequences such as remediation of damage caused. It is in the best interests of any company (and depending upon local rules, can be compulsory) to record discharged effluent characteristics such as pH at the point where it leaves their facility.