The cation differential pH and ORP sensors were designed for difficult applications where conventional sensors are ineffective. These include measurements such as brine solutions to applications as diverse as electrolysis processes and cheese manufacturing.
The problems experienced in these applications most often relate to the reference cell and are the result of either:
Yokogawa’s cation differential sensors feature a sealed glass reference and do not have a liquid junction nor any electrolyte to come in contact with the process. Therefore, the sensors do not suffer from diffusion potentials or fouling, which ensures measurement stability while being virtually maintenance free. There are different versions of differential pH sensors available and the significance of the advantages they have to offer over a traditional electrode is appreciated only after regularly using a conventional reference electrode in these difficult applications.
The FU20-FTS is the newest development in pH sensor technology available from Yokogawa. This sensor combines the measuring technology of our 12 mm differential sensor and the ruggedness of the appreciated wide body FU20 design in one product.
As is common in the market, Yokogawa uses silver/silver chloride reference cells in its products. In a wide range of applications, this solution has proven very effective and remains a cost-effective solution.
The lifetime of the conventional sensors is highly dependent on regularly maintaining pH equipment. Frequent cleaning is required to eliminate reference poisoning. 70-80% of industrial users will fully benefit from using differential sensor technology in their high temperature and pressure applications.
|Measurement Theory||Cation Reference|
|ORP Range||-1500 to 1500 mV|
|Temperature Range||0 to 105°C (14 to 221°F)|
0 to 10 bar (0 to 145 PSIG) @ 25°C
0 to 5 bar (0 to 72 PSIG) @ 105°C
Wet scrubbers are used in utilities, paper mills, and chemical plants to remove sulfur dioxide (SO2) and other pollutants from gas streams. Undesirable pollutants are removed by contacting the gases with an aqueous solution or slurry containing a sorbent. The most common sorbents are lime, Ca(OH)2, and limestone, CaCO3.
Sodium chlorate is an inorganic compound with the chemical formula NaClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leave sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching paper.
Continuous technology improvement is ongoing in the pulp & paper industry to obtain the best possible performance. Problems at the wet end (stock preparation) can rarely be corrected downstream. That is why monitoring and controlling pH in pulp stock is critical to the paper making process. Essentially, at every stage in the manufacture of paper, correct pH values play a vital role.
pH measurement in brine solutions (for example NaCl solutions as found in electrolysis processes or cheese manufacturing) are difficult and inaccuracy and short sensor life are the key problems in these applications.
Current trend for increasing mercury awareness throughout the public sector has caused the government to take action. Recently, the Environmental Protection Agency (EPA) has focused their efforts on controlling mercury levels produced in various coal fired power plants. Based on information from several case studies, the EPA developed the Mercury and Air Toxics Standards to cut back mercury emissions. The most popular technology utilized by coal plants to meet the new standards is a scrubber which cleans the off gas from the combustion process. ORP sensors can further monitor the effluent from these scrubbers to ensure optimal mercury emission levels are achieved. By closely monitoring the mercury concentrations in the effluent, plant managers will be able to easily confirm their plants are meeting the EPA's standards.
The lifetime of a pH sensor has a significant impact on the overall annual costs of a pH measuring loop. Optimizing four key factors will decrease these costs and optimize process control and overall plant efficiency.
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