Case study - Wet electrostatic precipitators offer cost-effective solution for HZL

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Courtesy of Beltran Technologies, Inc.

An array of complex air pollution issues places the metallurgical industry among the largest potential sources of pollutants, and one of the most tightly regulated industrial sectors. One fully integrated, nonferrous metal producer in India, however, is demonstrating that a company with a determined commitment to environmental protection, energy efficiency and sustainability can succeed in realizing those goals while remaining highly profitable -- provided it makes smart choices in emission control strategies and equipment.

Hindustan Zinc. Ltd. (HZL), headquartered in Udaipur, is India's largest and the world's second largest integrated producer of zinc and lead. Along with exploration, mining and power generation, the company maintains zinc smeller operations in Chanderiya. Debari, Rajpura Dariba and Vizag. Chanderiya is the largest such complex in the world. Hindustan Zinc's total metal production capacity recently topped 754.000 tons per annum (tpa) including 669.000 tpa of zinc. Revenues for 2009 were more than $1.26 billion.

The company maintains high environmental values in its operating structure, and in its state-of-the-art emission control technologies. Zinc-lead smelters can release an array of toxic pollutants into the atmosphere, including sulfur dioxide (SO,), respirable particulate matter (PM10), heavy metals (lead, mercury, arsenic, cadmium), dioxins. furans. hydrogen chloride (HCI). hydrogen fluoride (HF). sulfuric acid (H.SOj). ammonia (NH J and greenhouse gases.

To control smelter emissions. Hindustan Zinc has used scrubbers. cyclones and fabric filters. However, these were not sufficient to thoroughly clean the contaminated gas streams entering the sulfuric acid plants HZL built to capture and commercialize industrial quality sulfuric acid. In addition, more stringent regulations were issued by the Indian Central Pollution Control Board in 2006.

The company found a solution in wet electrostatic precipitators engineered by Beltran Technologies Inc.. of Brooklyn. NY. These precipitators offer several advantages ideally suited to the task, especially their ability to efficiently capture and remove fine, submicron-size particulate matter. Their low-temperature operation also makes them more effective on condensable sulfuric acid mists and VOCs.

Wet electrostatic precipitators (WESPs) utilize a high-intensity flow of ionizing electrons from a charged electrode toward a grounded collection surface. As the gas stream passes through this corona gradient, a charge is induced at the molecular level, propelling even submicron-size particles toward the collector, where they are captured and removed by a recirculating water spray.

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 the WESP to operate at up to 99.99 percent emission-control efficiency on submi-cron particulates, acid mists, organic pollutants — which was demonstrated at HZL's smelters.

Wet operation virtually eliminates the re-entrainment problems of dry WESPs and other technologies. It also eliminates the need for mechanical or acoustical rappers for cleaning the collection plates. There is minimal impedance or pressure drop compared to scrubbers and other methods. This allows faster throughput, and simpler, smaller-scale, and less expensive componentry. The superior performance of the Beltran WESPs has resulted in more effective cleaning, greater efficiency per energy use. and lower total operating cost for Hindustan Zinc.

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