Case study - Beltran WESPs deliver superior gas cleaning performance for Zambia’s fast-growing copper industry

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Courtesy of Beltran Technologies, Inc.

The central importance of copper production to the Zambian economy is reflected in the fact that the value of copper exports in 2010, about $5.8 billion, accounted for 78 percent of the country’s total merchandise export earnings, and helped make it the seventh largest producer in the world. Capitalizing on a worldwide surge in copper prices and the coincident privatization of Zambia’s mining industries in 2000, the corporate owners of the Mopani Copper Mine in Zambia’s mineralrich Copperbelt Province began upgrading both production capacity and environmental control technologies.

In 2007 the Mopani operators engaged a former engineering subsidiary of Monsanto, Inc., to enlarge and modernize their sulfuric acid plant, which was designed to capture and commercialize industrial-quality sulfuric acid from off-gases produced by the mine’s smelting and refining operations. To maximize gas cleaning efficiency before gases enter the acid plant, the firm contracted with Beltran Technologies, Inc., of Brooklyn, NY, who designed and constructed two wet electrostatic precipitators (WESPs) at the site.

The Mopani copper smelter and refinery in the town of Mufulira utilizes pyrometallurgical processes, which produce high levels of sulfur dioxide, sulfuric acid mists, particulates and other emissions originating from the metallic concentrate. Zambia’s Ministry of Mines and Minerals Development has required the facility to reduce acid mists by 94 percent and particulates by 99.5 percent. The sulfuric acid plant, coupled with Beltran’s advanced WESP technology, has achieved these stringent reductions, accepting a load of 11 kg/hr of sulfuric acid mists while producing 244 metric tons per day of clean, commercially viable sulfuric acid product.

Before entering the acid plant’s drying tower, smelter and refinery off-gases must be cleaned of sulfuric acid mists, particulates and other impurities in order to prevent corrosion, fouling and plugging in downstream compressors, catalyst beds and other sensitive equipment, and to avoid the formation of a “black” or contaminated sulfuric acid end product.

Mopani had reverse jet scrubbers but these alone were not effective on acid mists and fumes. The Beltran WESPs, using specially designed electrodes, collection tubes and multistaged charging, were ideally suited to the task, especially with their ability to efficiently capture and remove acid mists and fine, submicron particulates containing metal oxides and other contaminants.

Beltran’s proprietary system is comprised of a tightly configured array of square grounded collection tubes enclosing negatively charged electrode rods that generate intense corona fields. As the source gas is passed through the array, the ionizing electrodes induce a negative charge in even the most minute, submicron-size solid and liquid particles, including condensable organic chemicals. The charge differential propels these materials rapidly toward the grounded collection surfaces, where they adhere as the cleaned gas passes through. The captured particles are purged from the tubes by recirculating water sprays; residues, including aqueous sulfuric acid, are collected for further use or disposal.

After decades of research, Beltran has developed a unique electrode geometry featuring star-shaped discharge points which can generate a corona field four to five times more intense than that of a standard precipitator. Engineered in a multistaged charging configuration, the high-intensity corona gradients produce ultra-fast particle migration velocities, resulting in extremely high collection efficiencies up to 99.99 percent. The system also enables faster throughput of specified gas volumes, with minimal impedance and less pressure drop compared to scrubbers. These superior operating efficiencies enable operators to achieve performance goals using simpler, smaller scale, less expensive equipment.

The saturated operating environment of the Beltran WESPs overcomes a technical problem often encountered with dry ESPs or those which use mechanical or acoustical vibrating rappers to dislodge captured particulates: the re-entrainment of particles from the collection surfaces back into the gas stream. The stronger particle adhesion and continuous aqueous flushing of the Beltran WESPs virtually eliminate this phenomenon. The elimination of mechanical rapping also reduces costs relating to maintenance, operating environment and the higher energy demands imposed by this equipment.

The corrosive nature of the Mopani smelter emissions required that special attention be given to the materials used in construction of the precipitators. Thus, the Beltran wet ESPs were fabricated using fiberglass reinforced plastic (FRP) and high nickel-chromium alloys. Although precipitators used in acid mist applications historically have been made with lead, Beltran engineers have found FRP components to be less expensive, easier to construct and maintain, and extremely corrosion resistant. The electrically conductive sections of the WESPs are made from a special, conductive FRP material. The high-voltage insulators are kept continuously clean using a purge-air system, further reducing maintenance costs.

The Zambian copper industry is projecting an annual production of 1 million metric tons by 2015 and 1.5 million tons by 2020, according to the mines ministry. As private investments continue to pour in and the Mopani mines ramp up activity, the operator has already contracted with Beltran Technologies for six more WESP installations to handle the increasing volume of smelter and refinery emissions at its acid plant.

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