The widest application of dimensionally stable metal anodes is in the chlorine-caustic industry where mixed metal oxide DSA® coatings are used almost exclusively worldwide. Chlorine producers take advantage of the high current density operation (10 to 15 KA/m2) that mercury cells attained. Economic reasons favored the commercial operation of DSA® in mercury cells. Anode structures are designed and fabricated specifically for the customers’ cell, based on dimensions and operating conditions. The use of DSA® has resulted in significant power savings; the elimination of some hazardous plant operations associated with the use of graphite anodes, increased production, and product quality.

Further improvements in structure designs coupled with development of new coatings generated more opportunities. Many mercury cell users incorporated computer control systems designed to optimize the anode adjusting activities. The target control parameter, measured as the K-factor, was reduced to 0.07 or lower. Productivity increased in terms of the amount of product generated during the life cycle of the DSA® coating.
This improvement has seen common performance level of over 500 tons of chlorine per square meter of anode area. The longer life cycle reduced the frequency of interventions by maintenance personnel, decreasing mercury exposure to workers and to the environment. Other developments indicate the potential for improvement that could double the performance level.
Power Savings The introduction of DSA® in mercury cells was justified primarily by the benefit of power savings. In test trials, the reduction in cell voltage with DSA® was close to one volt. This difference is equivalent to a savings in excess of 700 KWH per short ton of Cl2 at a current density of 10 KA/m2. Additional savings are evident from stable and predictable cell voltages over the life cycle of DSA® and the ability to operate at higher current density than graphite anodes. The ability to operate the DSA® anode at a reduced gap over the long term allowed utilization of computer controls with motorized frames for mercury cells. K-factor One common operating parameter used to judge and compare the performance of mercury cells is the K-factor. This number indicates the relationship between the cell voltage and the current density at which the cell is operating. Essentially, it is the slope of that line. The lower this figure, the lower the cell voltage and the power consumption for the cell. An equation used to calculate the factor is: Kf = (Cell Voltage – 3.15) Current Density The current density is calculated based on the circuit load (KA) and the anodic surface area (m2). The graph below illustrates the mercury cell voltage performance as a function of current density at various k-factors.
Productivity A commonly used parameter to measure and compare the productivity of DSA® is the amount of chlorine produced on the basis of tons of chlorine per square meter of anode area. This factor is a combination of the lifetime that the DSA® operate in satisfactory condition and the current density over that term. Aside from the type of coating used, the quality of the operating conditions (anode shorts, brine contaminants, etc.) will determine the productivity that DSA® can achieve.
De Nora provides anodes for different types of mercury cells under a lease or purchase program. Services for the anode structures include repair work and renewal of the DSA® coating. Technical assistance is available to train and support customers in the installation, use and operation of cells and anodes. Mercury Cell Products Best Available Technology for Cells DSA® Anodes