Forward-thinking metallurgical plant operators around the world constantly seek out more advanced exhaust gas recovery technologies, not only to meet increasingly strict environmental regulations, but also to achieve superior operating performance and to control maintenance and other costs in a competitive marketplace. One fully-integrated polymetal producer headquartered in Brazil has managed to put into practice a determined commitment to environmental protection, energy efficiency and sustainability while remaining highly profitable by making smart choices in emission control strategies and equipment.
In the turbulent corporate world of metal extraction, smelting and refining, it is rare to find a company that has survived intact since 1919, even more so to find one that has remained under the control of the same family for three generations. Votorantim Metais, part of the multiindustry conglomerate Votorantim Group, produces zinc, lead, aluminum, nickel, copper, cadmium and other minerals through its eight industrial units located in twenty Brazilian states and fourteen countries, including the United States. Today, Votorantim Metais is the fifth largest zinc producer in the world, with an annual production capacity of 730,000 tons in 2010. It is the world leader in zinc oxide, second largest in zinc dust, and produces other zinc-based or -derived products, including special high-grade (SHG) zinc, zamac, zincal 200, copper sulfate and 98 percent pure industrial sulfuric acid.
In March 2002, Votorantim Metais purchased Companhia Paraibuna de Metais for US $106.5 million, seeking to expand production capacity at a time of rising worldwide zinc prices, and to gain access to Paraibuna’s rich Vazante zinc mine near Juiz de Fora. As part of a campaign to incorporate a “zero waste” principle, the company has been expanding and adopting new, modern production techniques at the Juiz facility, including greater recovery of waste sulfur emissions at the site, and currently expects to produce 45,000 tons of marketable sulfuric acid.
Paraibuna, the previous owners of the Juiz de Fora smelter, had incorporated a metallurgical sulfuric acid plant to capture and commercialize industrial quality sulfuric acid originating from its fluidized bed zinc roaster. In order to purify the smelter emissions entering the acid plant, Paraibuna had used a variety of techniques, including Lurgi lead mist precipitators. However, these were not sufficient to thoroughly clean the contaminated gas streams. In addition, the Lurgi equipment suffered significant deterioration after years of operation due to the harsh, corrosive nature of the gas stream components.
In 1997, the company found a solution in a system of wet electrostatic precipitators (WESPs) engineered by Beltran Technologies, Inc., of Brooklyn, N.Y. These precipitators offered several advantages ideally suited to the task, especially their ability to efficiently capture and remove fine, submicronsize particulate matter emitted from the roaster. Their saturated, low-temperature operation also made them more effective on sulfuric acid mists and other condensable contaminants.
Most importantly for the projected long-term operation of the smelter and its acid plant, the Beltran precipitators were designed for durability, and were constructed using specially formulated fiber-reinforced plastics (FRP), a composite material made of a polymer matrix reinforced with fibers. These materials were used in sensitive surface areas and housings; a special conductive FRP was used for the WESP collector plates.
The Beltran WESPs were designed around an array of ionizing electrodes configured as star-shaped discharge points, surrounded by grounded collection surfaces. The unique geometry of the Beltran system generates a corona field 4-5 times greater than that of ordinary wet or dry ESPs. The intense corona induces a strong negative charge in even the most minute, submicronsize gas-stream particles, propelling them toward the collection plates, where they adhere as cleaned gas is passed through. The captured particles are cleansed from the plates by recirculating water sprays. The cleaned gas is ducted to the acid plant. The wet collection surface prevents re-entrainment of particles and facilitates clean, safe handling of waste slurry, with minimal energy penalty compared to other methods. The multistage system uses two 10 x 14 WESP modules in series for maximum effectiveness, and processes 43,000 Nm3/hour.
At the Paraibuna zinc smelter, the Beltran WESPs have been operating for over 15 years at 99.5 percent cleaning efficiency on fine particulates and acid mists. This level of purity is essential not only to protect the integrity of the downstream acid plant components, but to assure the quality and consistency of the final sulfuric acid product—a valuable industry commodity with hundreds of uses.
It is important for engineers to recognize that there are key differences in features and benefits offered by the various precipitator systems. Although they may share similar operating principles and basic structures, WESPs can vary greatly in design, materials, gas flow rate, durabilityas well as collection efficiency. Beltran’s advanced wet electrostatic precipitators are the ideal solution for the complex, exacting emission control needs of any ferrous or non-ferrous metallurgical facility, offering the following unique advantages:
- Proprietary electrode design generates extremely intense electrostatic fields and captures particulates and other pollutants down to submicron diameters, with up to 99.9 percent efficiency.
- Aqueous flushing of collectors defeats particle re-entrainment, resistivity and stickiness, and reduces energy input.
- Low-temperature operation captures condensable compounds and dramatically increases gas cleaning efficiency.
- Effective on: fine particulates, SO3, HCl, oily aerosols, sulfuric acid mists, condensed organics and heavy metals (cadmium, chromium, lead, manganese, nickel).
- Unsurpassed gas cleaning for roasters, smelters, furnaces and sintering plants.
Beltran’s advanced wet electrostatic precipitators have given Votorantim’s zinc operations at Juiz de Fora a definitive economic and technical edge in an increasingly competitive field.