Feature
Sulfuric acid gas & mist cleaning: wet electrostatic precipitators for superior performance By Gary Siegel, Marketing Director, Beltran Technologies Inc.
Industries that generate sulfur oxides and sulfuric acid include metallurgical smelters and refineries, petroleum refineries, natural gas processing facilities, electric generating units, spent acid regeneration plants, and municipal waste incinerators. In many cases, a common and cost-effective solution for capturing and utilizing sulfur oxides and corrosive sulfuric acid emissions is to have a downstream sulfuric acid manufacturing plant. Operators of these facilities can take advantage of the high industrial market value of purified sulfuric acid, a primary industrial chemical used in fertilizer manufacturing; mineral processing; petroleum refining; wastewater processing; the manufacture of paints, dyes, detergents, lead batteries, and explosives; and the synthesis of other chemicals, as in the alkylation of gasoline additives. An efficient sulfuric acid manufacturing process strictly requires the removal of contaminants from the input gas streams, especially fine particulates and acid mists such as those emitted from metal ore roasters and smelters, petroleum refineries, and coal-fired industrial boilers. This is necessary for protecting downstream components such as catalyst beds from corrosion, fouling, and plugging, as well as for preventing the formation of a “black” or contaminated acid end-product. Proper gas cleaning also results in lower maintenance and operating costs for affected industries. For removing fine particulates, acid mists, and other contaminants from the gas stream, the one technology that is almost universally specified for this application is the wet electrostatic precipitator (WESP). Primarily targeted at capturing submicron-scale particulate matter, saturated sulfuric or other acid aerosols, and condensable organic chemicals, the advance designed Beltran WESP system is often specified to be incorporated after the gas scrubbers, and can achieve collection efficiencies including submicron particulate matter of greater than 99.9%—far superior to other equipment. However, 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 the similar operating principles and basic structures, WESPs can vary greatly in design, materials, gas flow rate, durability—as well as collection efficiency. A basic WESP is comprised of an array of ionizing electrodes such that negatively charged discharge rods generate a PAGE 28
Mopani Copper Mines currently has nine Beltran WESPs for sulfuric acid gas cleaning at their copper smelter plants in Zambia, Mufulira, and Kitwe.
strong electric field and corona. These are surrounded by or interfaced with positively charged or grounded collection surfaces, which attract and hold the charged particles. In operation, the source gas is passed through the electrode array, which induces a negative charge in even the most minute, submicron-size particles, propelling them toward the grounded collection surfaces, where they adhere as the cleaned gas passes through. The captured particles
are cleansed from the plates by recirculating water sprays; residues, including aqueous sulfuric acid, are extracted for further use or disposal. The cleaned gas is ducted to downstream equipment or to the stack, depending on the application. A traditional problem has been with high-resistivity contaminants, such as lowsulfur coal ash. However, Beltran WESP configurations and designs can overcome this challenge. The system is engineered
At the Hindustan Zinc Acid Plant in India, Beltran WESPs virtually eliminate particulate re-entrainment acheving 99.9% collection efficiency and faster throughput.
with multistage ionizing rods, star-shaped discharge points, and space-saving hexagonal tube designs. This unique geometry generates a corona field 4-5 times more intense than other ESPs, achieving superior collection efficiency on resistant materials. These features also allow higher velocity gas streams, resulting in faster throughput. WESPs impose a significantly lower pressure drop compared to scrubbers, and also contribute to increased production speeds. Furthermore, these gains in efficiency enable the use of smaller-scale, less-expensive equipment for a given set of operating parameters. Another challenge for traditional precipitator designs was the re-entrainment back into the gas stream of particles from the collection surfaces. Dry-operating ESPs, especially those using mechanical or acoustical vibrating rapper machinery, are particularly susceptible to this phenomenon. Precipitators based on wet operation, however, minimize re-entrainment, as the aqueous flushing is continuously effective. The elimination of mechanical rapping also reduces the higher cost and energy drain imposed by that equipment. Other critical features to look for in WESP equipment are the more advanced electronic controls, which can optimize operating parameters such as gas flow, saturation, temperature, and corona intensity to achieve maximum efficiency.
Superior technology for wide applications
Because it operates at cooler temperatures—usually at the process gas saturation temperature between 100-170° F—the WESP is uniquely adept at capturing condensable organic materials and acid mists, making this technology an invaluable component for sulfuric acid production plants. Since sulfur is a common element found in the earth, sulfuric acid and other sulfurbased pollutants are most associated with industrial processes that deal with materials originating underground. These industries include: • Metals and metallurgical plants (mining and extraction; smelting and refining; finishing and metallurgical processing such as steelmaking, alloys, etc.) • Fossil fuels (petroleum refineries/processing or fossil fuel-fired power generating units) For more information, contact Beltran Technologies, Inc. at info@beltrantechnologies. com or visit www.beltrantechnologies.com. q Sulfuric Acid Today • Spring/Summer 2021
