AngloGold Ashanti chooses Beltran WESP - Case Study
AngloGold Ashanti Brasil Mineracao is a leading producer of gold in the world. AngloGold was working on production plans for the Cuiaba Gold Mining Expansion Project located at Nova Lima, Minas Gerasis. The plant's production capacity is projected to be equivalent to 400 metric tons of sulfuric acid per day. The Promon Company worked on the design, procurement, construction and assembly services for the sulfuric acid plant that converts the sulfur oxide (SOx) produced as a byproduct of gold mining into sulfuric acid for sale in the marketplace, while also preventing its release as a gas into the atmosphere. AngloGold Ashanti sells sulfuric acid mainly to manufacturers of paper pulp, fertilizer and chemicals. AngloGold Ashanti's Cuiaba Expansion Project involved expansion of an existing unit with a goal for production of up to 6 tons of gold per year.
The facility has selected a wet electrostatic precipitator (WESP) engineered by Beltran Technologies, Inc.. of Brooklyn. NY, to clean the gas of impurities (mainly As. Hg, Cu, Fe, Zn, Cd, Pb, CI. Mn, Ti. Cr. S03, and sulfuric acid mist) before it enters the sulfuric acid plant. The Beltran WESPs offer several advantages ideally suited for the task of gas cleaning, especially the ability to efficiently capture and remove very fine sub-micron particulate and acid mist.
The corrosive nature of the flue gases demands special attention for the materials of construction of WESPs. The Beltran WESPs are fabricated using fiberglass reinforced plastic (FRP) and high nickel-chromium alloys. While historically many electrostatic precipitators used for acid mist applications have been constructed from lead. FRP precipitators are less expensive, easier to construct and maintain and are extremely corrosion resistant. The electrically conductive sections of the WESP are made from special conductive FRP. The system has achieved an overall efficiency of greater than 99 percent.
To prevent the formation of 'black' or contaminated acid and to protect the catalyst beds from fouling and plugging. Beltran WESPs are used to clean the off-gases before entry into the acid plant. The acid plants that must handle impure sulfur dioxide gas such as those emitted from metallurgical processes like ore roasters, flash smelters and spent acid regeneration, require the removal of acid mist, residual dust and fumes before the gases enter the drying tower.
Conventional scrubbing systems (wet or dry) are generally not effective in controlling sub-micron emissions, consisting primarily of acid gas mists, sub-micron particulates and condensed organics. Wet tubular electrostatic precipitators, because of their ability to generate multi-staged charging and strong electrical fields in a wet, cooled atmosphere, have been shown effective in cleaning the flue gas.
The Beltran WESPs use ionizing rods with star shaped discharge points in a square or hexagonal configuration. This unique geometry generates a corona field four to five times greater than other wet or dry ESPs. This enables Beltran WESPs to operate at up to 99.9 percent emission control efficiency on sub-micron particulates and acid mists, which was demonstrated at AmzloGold.
Wet operation virtually eliminates the re-entrainment problem of dry ESPs and other technologies. It also eliminates the need for mechanical or acoustic rappers for cleaning the collection plates. There is minimal impedance and pressure drop compared to scrubbers and other methods. This allows faster throughput, a simpler, smaller scale and less expensive components. The superior performance of Beltran WESPs has resulted in more efficient cleaning, greater efficiency, greater efficiency per energy use and lower total operating cost for AngloGold.