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Monitoring Electrolytic Cell Anode Current Increases Current and Energy Efficiency

In 2011, five-and-a-half-million tons of aluminum were produced in the United States. Over two-million tons were produced in smelters, large electrolytic cells used to convert aluminum oxide to aluminum. Smelter pots emit fluorinated hydrocarbons, CF4 and C2F6, which have global warming potentials of 6,500 (i.e., 1 ton of CF4 has the global warming effect of 6,500 tons of CO2) and 9,200, respectively. These emissions occur mostly during a pot upset condition that is known as an "anode effect." This effect occurs when gases emanating from the anode, separate it from the electrolyte by a gas film and cause polarization. The effect can be characterized by a sudden increase in voltage. Energy efficiency is another area of opportunity for improvement. Converting aluminum oxide to metal in large electrolytic cells requires hundreds of thousands of amps, and the cells typically operate with an energy efficiency of only 45%-50%, providing scope for efficiency improvements.

With assistance from AMO, Wireless Industrial Technologies Corporation (WIT) developed a wireless monitoring system for detecting and controlling anode effect in electrolytic cells used in aluminum production. The system can provide early warning by 20 seconds up to several minutes before an anode effect occurs. WIT's system uses a master-slave array of Hall effect sensors to monitor changes in current flow through the anodes. In addition to detecting anode effects, WIT also has investigated and determined how anode current distribution affects current utilization efficiency (cell productivity), and overall energy efficiency of the cell. By monitoring current distribution symmetry versus skewness throughout the cell, the current utilization efficiency could be improved and the current distribution could be adjusted during anode "warm up," which is required when a spent anode is replaced. WIT has field tested its wireless system in several aluminum smelters with positive results. The wireless nature of the system is noninvasive and meets the strict safety and electrical hazards policies of an aluminum production plant. WIT estimates energy savings up to 5% or ~3.25 trillion Btu per year domestically. Eliminating anode effect events could potentially reduce greenhouse gas emissions by 0.8 tons CO2 per ton of aluminum produced.

Diagram of placement of wireless sensors in relation to the anodes.

Overview

Applications

Can be used in producing aluminum or other metal production facilities that use electrolytic cells, e.g., zinc and nickel.

 

Capabilities

  • Provides wireless communications, allowing noncontact monitoring and control.
  • Provides real-time measurement of multiple process parameters including current, voltage, and temperature.
  • Achieves early detection of anode effect.

Benefits

 

Efficiency and Productivity

Improves cell productivity and current efficiency by providing crucial information about current distribution and anode status.
 

Emissions

Reduces greenhouse gas emissions by improving electrolytic cell operation and increasing energy efficiency.
 

Installation

Provides safe installation by using wireless communications and eliminates exposure to electrical hazards associated with running signal wires.

 

Contact Information

J. W. Evans
(510) 813-5877
jim.w.evans@gmail.com
Wireless Technologies Corporation

 

Methodology

Review the methodology used to collect information about AMO funded technology development and estimate energy use and cost savings and emissions reductions.

Last updated: August 2014