Pollution Engineering - November 2008 - (Page 42)

Wet benefits benefits. benefits. First, it encourages condensation of encourage water on the inside of the collecting tube, enhancing particulate collection and making it easier to remove the collected particulate matter. Second, it provides a source of warm air that can be used for a variety of purposes, including purge air for the support insulator compartments, which saves energy. High-frequency power supplies. The development of high-frequency power supplies has been beneficial to all electrostatic precipitators. However, the benefits to wet ESPs may be the greatest because of the costly materials of construction in wet units and because of the tendency of wet units to be applied to gas streams with high concentrations of fine particulate. As seen in Figure 2, the high-frequency power supply outperforms the standard 60-Hz, single-phase design. The additional voltage means that the precipitator can be smaller for the same efficiency or, alternatively, perform better at the same size. Multiple, vertical stages. Multiple elec- “ While there is still a lot of operating experience to be gained, the development of wet ESPs made from an entire range of materials has opened up an equally wide array of applications. New materials. When Congress passed the 1970 Clean Air Act, wet ESPs for acid mist service were made exclusively of lead. In a few other applications, carbon and 300-series stainless steels were used. Today, modern alloys ranging from duplex stainless steels all the way up to high nickel alloys are commonplace. Also, fiberglass, PVC and other polymeric construction have been employed. tric fields in series are nothing new in dry ESPs; units with three or more fields are the rule in coal-fired boiler applications. However, vertical fields in series in wet ESP designs are a new development, one which has delivered some surprising performance improvements. These multi-field installations have shown outlet particulate concentrations that rival levels achieved by the best fabric filtration systems. Also, field testing has shown that for a given level of efficiency, the total required collecting area of a multi-field wet ESP is significantly less than a single-field unit. ” New applications Perhaps the most important new application for wet precipitators is as a final gas-cleaning step for coal-fired utility boilers. Presently there are five utility-scale wet ESP systems operating in North America and several more in engineering and construction. These units are mostly intended to control the sulfuric acid mist that is emitted downstream of a wet flue gas desulfurization (FGD) scrubber. The need for an acid mist-control step is further amplified by the effect of upstream selective catalytic reduction systems designed to reduce NOX emissions. This is because these systems tend to add SO3 to the gas stream, which ultimately hydrates to H2SO4 in the FGD scrubber. A related application presently being explored is directed toward cleaning coalfired utility boiler flue gas prior to entering a system designed to remove CO2. The role of the wet ESP is critical in this process if the CO2 is to be absorbed in a highly alkaline liquor such as ammonia. In such a process it is extremely important to remove the acid mist before the gas enters the CO2 absorber. Otherwise, the recirculated alkaline reagent will be wasted as it reacts with the acid mist. Another innovative application of wet ESPs has been in the biofuels industry. In the manufacture of ethanol for fuel, the solid material left behind from the fermentation tanks (distillers grain) is normally dried so Trying to manage your environmental data with ancient tools? • Over 200 consultants and 300 labs manage data from over 150,000 facilities using EQuIS™ • Advanced ArcGIS Integration • Sample Planning Module with Completeness Checker • World’s Premier Lab Data Checking System • Build – Serve – Push Reports and Graphics over the web • World-class Help Desk info@earthsoft.com (978) 369-2201 www.earthsoft.com 42 Pollution Engineering NOVEMBER2008 PLE09084Eart.indd 1 8/8/08 9:46:30 AM http://www.earthsoft.com http://www.earthsoft.com

Table of Contents Feed for the Digital Edition of Pollution Engineering - November 2008

Pollution Engineering - November 2008 Contents The Editor's Desk EnviroNews PE Events Legal Lookout Casebook Canada Environment Management The Green Files Waste Island Phase I ESAs and Vapor Intrusion Meeting the Mercury Target Wet ESPs - The Sky's the Limit Most Successful IFAT China Ever Thermoplastic to the Rescue Install a Trench Without Open Excavations Remediate Impacted Soils Without Accumulation of Metabolites Apply an Alternative to Wet ESP Solve These Common Pump Problems Minimize Risks Handling Ammonia Monitor International Regulatory Developments for Audits Skim Oil and Save Prevent Chemical Vapor Intrusion Spill Control and Containment Products Pumps and Systems Equipment PE Products Classified Marketplace Advertisers Index State Rules

Pollution Engineering - November 2008

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