United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-92/058 May 1992 EPA Project Summary Controlling Odorous Emissions from Iron Foundries Gerhard Gschwandtner and Susan Fairchild The main process sources of odors in an iron foundry are (1) mold and core making, (2) casting, and (3) sand shakeout. The odors are usually caused by chemicals, which may be presenlt as binders and other additives to thei molding sand, or as breakdown prod- ucts when these chemicals are sub- jected to molten iron as it is poured into molds. There are many binder for- mulations; typical formulations arei based on using some form of an oil,, urethane, formaldehyde, phenol, or fu ran. Common additives include coal;) cereals and starches, clays, and refrac- tory minerals such as silica. A great many possible compounds can bei formed when these chemicals are ex- posed to molten iron. Common parr ticulate removal technologies may alsoj reduce odors, although the odors are> probably caused by vapor-phase com- pounds that are not well controlled by cyclones and bag filters. Carbon ad- sorption may be effective but might also be very expensive. Wet scrubbers with special additives in the water may be more effective but have drawbacks! such as generating a waste water treat- ment requirement and the potential for corrosion. Another technology report- edly used in Europe is biofiltration. This Project Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Tri- angle Park, NC, to announce key find- ings of the research project that is fully documented In a separate report of the same title (see Project Report ordering' Information at back. Introduction The control of industrial odor can be difficult. The choice of a control method depends on many technical and economic considerations. The chemical characteris- tics of the odorous pollutant, the volume of emissions to be treated, and the manu- facturing process are only a few consider- ations. There are many types of odor con- trol, including masking, various removal techniques, and process modifications. This report describes several removal tech- niques including wet chemical scrubbing, biofiltration, adsorption, and new emerg- ing techniques. The adaptation of these controls to a particular process can be complicated and requires careful planning. Many pollutants have low odor thresh- olds and require the removal of extremely small concentrations from large volumes of air. This is technically difficult and may require huge amounts of energy, capital investment, and large control devices de- pending on the options selected. Further- more, odor may not be completely con- trolled, arid some level of odor may per- sist despite the addition of controls. Once the decision is made to control odor, the course of action may be deter- mined by the availability of water, energy, and waste water treatment facilities. Most control methods employ water sprays, tanks,-and mists to trap water-soluble chemicals and particulate. In the absence of sufficient quantities of water, it may be necessary to consider using other meth- ods such as carbon adsorption or biofiltration. Printed on Recycled Paper ------- Discussion Sources of Odorous Emissions in Iron Foundries In an earlier report, the U.S. EPA iden- tified major sources of air toxic pollutant emissions in iron foundries. Of these pol- lutants, organic compounds are the most odorous, although metals and dust may also be sources of odor. The main sources of organic emissions in iron foundries are mold and core making operations, casting operations, and sand shakeout. Mold and core making may be subdi- vided according to resin sand operations, commonly referred to as shell molding, green sand operations, and stack mold- ing. In general, these processes have the greatest potential to release odors because of the relatively high concentrations of or- ganics in the uncontrolled emissions. Most organic emissions originate from the casting process when molten metal is poured into a mold. During this process, chemical reactions involving various binder ingredients are driven by the intense heat of the molten metal. The resulting gas- eous emissions may be the products of numerous reactions of the initial binder ingredients, the products of decomposi- tion, and the reactions among the prod- ucts of decomposition. In addition, fine particulate matter is released during cast- ing. PMt? emission factors range from 2,500 to 4.2 x 10* mg/Mg of metal poured. Foundry dust typically contains inorganic emissions such as nickel, lead, boron, and chromium, depending on the composition of the poured metal and its impurities. The uncontrolled removal of castings from sand molds during the sand shakeout process releases moisture, dust, resin and binder fumes, and products of thermal de- composition. Information on volatile organic compound (VOC) emission factors is rare, but some information is available for par- ticulate, matter that suggests a wide range of PM)0 emissions from 85 x 103 to 9 x 106 mg/Mg of iron castings. Most odorous emissions originate from mold and core making operations and from casting operations. These emissions re- sult from the use of chemical binders and resin and sand additives. Odor Thresholds The threshold concentration for odor de- tection and recognition varies from person to person and from compound to com- pound. Many articles have been written on odor evaluations and threshold values. Odor detection varies depending on the compound being evaluated and on the presence of other compounds that may mask or enhance the odor. Some com- pounds may be offensive even in low con- centrations, especially certain sulfur com- pounds, while others, such as certain es- ters, may be less objectionable. Determining Acceptable Levels of Odors Due to the subjective nature of odors, it is difficult to establish an acceptable level of exposure, especially when many com- pounds and emission sources are involved. Ideally, the concentration of an odorous compound should be below the odor threshold. While emission controls help reduce the odor, some pollutants such as thiols (mercaptans) require virtual elimina- tion before they are undetectable. Objective evaluation of an odor should be the first step in controlling it. ft is im- portant to know which compound or com- binations of compounds is causing the odor. Usually, an independent, third-party assessment of unwanted odor is neces- sary to form an objective conclusion. Both on-s'rte and community surveys can pro- vide important information for identifying sources of the odor, establishing condi- tions that elicit complaints in the affected community, and confirming odor levels pre- dicted by source sampling, analysis, and atmospheric dispersion estimation tech- niques. Selecting a Control Efficiency Not all odorous compounds may be suf- ficiently controlled with the same control device. For example, one compound may require only 99% control efficiency while another may require 99.999% control effi- ciency to reduce the concentration below its odor threshold value. In this case, two different control devices may be needed to solve the odor problem. Rather than attempting to reduce all odorous emissions simultaneously, reason- able available control technology should be applied first to reduce total emissions, including particulate matter and organic compounds. In addition, the dispersion and dilution of the emissions should be en- hanced to the maximum extent possible. A comprehensive approach to controlling foundry emissions is better than control- ling each odorous pollutant individually. Selecting the Best Control Option Several methods are available for con- trolling odor from iron foundries. Aside from reducing overall emissions and good operating practices, emission control tech- nologies that are applicable to iron foundry processes include: • Fabric filtration • Adsorption (activated charcoal) • Wet scrubbers with chemical additives • Biofiltration • Photocatalytics and oxidization There are several basic considerations when selecting one of these control tech- niques for an iron foundry. The ideal tech- nology would be one that does not require water, energy, or maintenance, costs little, effectively removes many different odor- ous compounds, and produces no solid or hazardous waste. The ideal technology would also not interfere with existing pro- cess operations and conditions. Fabric filtration is essential to remove sand and other fine particulate matter and should be used first before controlling or- ganic compounds by other means. The control efficiency of various types of wet scrubbers can be enhanced by using vari- ous chemical additives. The ideal additive is one that creates harmless waste in small quantities, does not affect process equip- ment, and does not require special treat- ment, conditioning, or monitoring. Selection of a chemical additive requires judgment and knowledge about the chemi- cal reactions with the targeted pollutants. Many companies can recommend and sup- ply chemical additives usually in conjunc- tion with a particular type of scrubber. The particular requirements should be care- fully analyzed beforehand, and all aspects of the wet scrubber (including waste dis- posal, supply requirements, and system operation and maintenance requirements) should be considered. Incineration, thermal oxidation, and cata- lytic oxidation are generally not suitable to iron foundries because of the large air flow rates. Odor masking, a technique where a stronger pleasant odor is added to the exhaust stream, generally has not provided consistent and satisfactory re- sults. Deciding What Is Feasible and Reasonable Many environmental regulations use the words "feasible" and "reasonable" when describing control requirements. In the case of odor control, specific requirements are often unclear and left to interpretation. Since the ideal control technology does not exist, iron foundry operators wishing to control odorous emissions must accept some level of inconvenience or expense. This report provides basic information that can be used in comparing and selecting a control technology. Whether a technology is feasible or rea- sonable depends on the circumstances of the foundry. For example, shortage of wa- ------- ter would eliminate many of the traditional elude the use of certain chemical adcli- advantages over older, traditional systems wet scrubbers described in this report. tives in wet scrubbers. and should be considered. These new The need to reduce maintenance costs, As technology changes, better and methods have been tried and proven at for example, might preclude the use of proven systems may become available. many different industries here and abroad carbon adsorption, while the lack of on- Currently, atomized mist scrubbers, and can be adapted to the major sources site waste disposal facilities might pre- biofiltration, and photocatalytics offer many of odor at iron foundries. •&V.S. .GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40253 ------- Gerhard Gschwandtner and Susan Fairchild are with E. H. Pechan and Associates, Durham, NC 27707. Robert a McCrlllls is the EPA Project Officer (see below). The complete report, entitled "Controlling Odorous Emissions from Iron Foundries," (OrderNo. PB92-166 925/AS; Cost: $17.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 Official Business Penalty for Private Use $300 EPA/600/SR-92/058 ------- |