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HomeMy WebLinkAboutNCD980602163_19810901_Warren County PCB Landfill_SERB C_Civil Engineering - Thermal destruction options for controlling hazardous wastes-OCR; I I: I I I . l l I ; I ! I · I j l f Thermal destruction -options for controlling hazardous wastes The growth rate for the volume of hazardous wastes produced in this country alone requires new and efficient methods of waste disposal. Incineration, has demonstrated efficiency and safety in its use thus far. E. TIMOTHY OPPELT Chief United States EPA Cincinnati, Ohio THE HAZARDOUS WASTES generated an- nually in the United States by over 270,000 industrial plants and facilities could fill the New Orleans Superdome five times,every day. Over the last decade, controlled high-temperature incineration has .emerged as an effective alternative to the more traditional disposal methods of landfilling, ocean disposal and deep-well injection. · The U.S. EPA estimates that there may be as many as 850 incineration facili- ties in the U.S. today. The vast majority are located on industrial plant sites with roughly a half dozen located on off-site commercial plants. A recent EPA study forecasts that these off-site facilities could increase in capacity by as much as 55% in 1981 and by another 43% in 1982 if current waste management plans are executed. EPA encourages incineration in prop- erly designed and operated facilities as the preferred control technology for com- bustible organic hazardous wastes. Al- though only 15% of hazardous wastes is now incinerated, as much as 50% of haz- ardous wastes generated in the U.S. could be handled by this method. Incineration is capable of destroying the hazardous nature of organic wastes, while reducing · volume, and in many cases, recovering some energy produced in the combustion process. Tests conducted by EPA and others have shown tha( complete destruction of a wide range of hazardous wastes can be achieved safely with existing technology. providing proper design and operating parameters are employed. An EPA survey of United States and · international . technical literature identi- fied 43 incinerator /waste combinations for which a waste destruction efficiency of 99.99% or greater was achieved in doc- umented test burns. The hazardous wastes tested included pesticides, polych- lorinated biphenyls (PCBs), and other chlorinated hydrocarbons known within the scientific community to be among the most difficult materials to destroy by incineration. Incineration also poses problems, due· to potential for air emissions of uncom- busted waste or hazardous combustion byproducts. The control of fugitive emis- sions of hazardous compounds from in- complete combustion or during storage and transfer operations may also pose an important consideration. Recognition of the environmental ad- vantages in the use of incineration for hazardous waste destruction balanced against the potential problems of improp- er incineration practice led the EPA to develop recently-published Interim and Proposed Standards for hazardous waste incineration facilities (January 23, I 98 I). These regulations require owners and operators of facilities to obtain a permit to incinerate the specific hazardous wastes to be handled. The facility must meet three basic standards: • 99.99% destruction and removal effi- ciency (DRE) for each principal organ- ic hazardous component (POHC) of the waste feed • 99% removal of hydrogen chloride from the exhaust gas (for wastes con- taining more than 0.5% organically bound chlorine) • an emission limit no more than 180 milligrams particulate matter per dry standard cubic meter of exhaust gas The incinerator operating conditions that · are shown to achieve these performance standards then become the conditions of the permit and form the basis for enforc- ing compliance. While these performance requirements are believed to be protective of public health and the environment in the majori- ty of instances, the EPA has also pro- posed standards by which requirements could be modified on the basis of risk assessment of the facility. These stan- dards, if adopted, would enable consider-_ ation of the specific impact of the facility size, proximity to populated areas, and in particular, the relative hazards of differ- ent wastes to be incinerated. Incineration process Incineration is an engineered process that employs thermal decomposition via thermal oxidation at high temperature (900°C and greater) to convert a waste to a lower volume, nonha7.ardous materi- al. The \i:aste, or at least its hazardous components, must be combustible in or- der to be destroyed. The primary prod- ucts from combustion of organic wastes are carbon dioxide (CO2), water vapor, and inert ash. However, there are a multi- tude of other products which may be formed. Hydrogen chloride (HCI) and small amounts of chlorine (Cl2), for example, are formed from the incineration of chlo- rinated hydrocarbons. Hydrogen fluoride (HF) is formed from the incineration of organic fluorides, and both hydrogen bro- mide (HBr) and bromine (Br2) are formed from the incineration of organic bromides, to cite just a few examples. Suspended particulate emissions are also produced and include particles of mineral oxides and salts from the mineral constit- uents in the waste material, as well as fragments of incompletely burned com- bustibles. By-products from the incineration of hazardous wastes may also result from incomplete combustion and as products of combustion of constituents present in wastes and air. Products of incomplete combustion (PICs) include: carbon mon- oxide, hydrocarbons; aldehydes, :ketones, amines, organic acids, polycyclic organic matter (POM), and any other particles which escape thermal destruction. In a well-designed incinerator, these products are insignificant in amounts. However, in inadequate systems, PICs may pose environmental concerns. Po- lychlorinated biphenyls, for instance, are known to decompose under such condi- tions into highly toxic chlorinated diben- zo furans (CDBF). The hazardous mate- rial, hexachlorocyclopentadiene (HCCPD) 1 found in many hazardous wastes, is known to decompose into the even more hazardous compound, hexach- lorobenzene (HCB). Air emission control devic~s have been designed to limit emission of hazardous by-products. Afterburners are used to control emission of unburned organic by- products by providing additional combus- tion volume at an elevated temperature. Scrubbers are us.ed to physically remove particulate matter, acid gases, and residu- al organics from the combustion gas stream. Design and operation The most important factors for proper incinerator design and operation are com- bustion temperature. combustion gas res- idence time; and the efficiency of mixing waste with combustion air and auxilliary fuel. Chemical and thermodynamic proper- ties of the waste that are important in determining its time/temperature re-/ Fig. 1 Liquid injection incinerators are applicable almost exclusively for pumpable liquid waste. quirements for destruction are its ele- mental composition, net heating value,. and any special properties (e:g., explosive properties) that may interfere with incin- eration or require special design consider- ations. The percentages of carbon, hydrogen, oxygen, nitrogen, sulfur, halogens, and phosphorus in the waste, as well as the moisture content, need to be known to determine stoichiometric combustion air requirements and to predict combustion gas flow and composition (factors in air emission control system design). In general, higher heating values are required for solids versus liquids or gases, for higher operating temperatures, and for higher excess air rates-if combustion is to be sustained without auxiliary fuel consumption. While sustained combustion is possible with heating values as low as 4000 Btu/lb (2222 calories/gram), in the hazardous waste incineration industry it is common practice to blend wastes (and fuel oi}, if necessary) to an overall heating value of 8000 Btu/lb ( 4444 calories/ gram) or more. Blending is also used to maintain the net chlorine content of chlorinated haz- ardous waste to a maximum of roughly 30% by weight to limit free chlorine con- centrations in the combustion gas. Predicting time/temperature require- ments for achieving the 99.99% POHC destruction and removal efficiency stan- dard (DRE) is a very difficult task. While highly halogenated materials are more difficult to destroy than those with low halogen content, data on specific waste/ incinerator /operating condition combina- tions are only just beginning to emerge. Extensive research and testing are planned or underway in the EPA as well as in the private sector. In the interim, · however, most facilities will need to cons duct trial burns to determine the specific operating conditions necessary to achieve the DRE requirement for classes of waste they handle. Ongoing EPA research is working to establish classes of waste and POHCs based upon the difficulty (i.e., severity of the combustion conditions) in achieving the 99.99% DRE requirement.. Ultimately, this hierarchy of waste and POHC incinerability will be used to com- pare proposed operating conditions for untested waste/incinerator combinations with existing trial burn data to minimize the number and cost of future permit trial burns. Mixing is also an important design and operating factor. Adequate mixing in- sures that waste, hot combustion gases and combustion air come into intimate contact and that all waste particles have adequate residence time in the combus- tion zone to allow destruction to occur. This is accomplished by the use of high efficiency burners, the atomization of waste liquids into fine droplets (usually to 40µ in diameter or less), and the control of excess combustion air to maintain ade- quate turbulence in the combustion reac- tor. Basic technology Two types of technology dominate the incineration field, liquid injection or rota- ry kiln incinerators. Over 90% of all incineration facilities incorporate one of these technologies. Of these, more than 90% are liquid injection units. Remaining incinerators include fluidized bed;; and starved air /pyrolysis systems. Liquid injection incinerators, as the name implies, are applicable almost ex- clusively for pumpable liquid waste. See Fig. I. Vertically aligned liquid injection incinerators are preferred when wastes :I .I I l l I j I -I I I i 1 .. Fig. 2 Rotary kilns are versatile units often used for commercial off-site facilities. are high in inorganic salts and ash con- tent, while horizontal units may be. used with low ash wastes. Rotary kilns are more versatile incinerators as they are applicable to the destruction of solid wastes, slurries, and containerized waste as well as liquids. Because of this, these units are most frequently used for com- mercial off-site facilities, such as the Cin- cinnati Metropolitan District facility shown in Fig. 2. All hazardous waste incineration facili- ties generally require some form of com- bustion gas clean-up. Venturi scrubbers, packed bed scrubbers, or plate tower scrubbers are used for particulate and gaseous pollutant control at the majority of hazardous waste incineration facilities. Complete engineering descriptions of these and other hazardous waste incinera- tion facility evalua.tion procedures are included in the recently-published, EPA Engineering Handbook on Hazardous Waste Incineration. Alternative options While the practice of controlled high temperature incineration in specially de- signed hazardous waste disposal facilities is expected to increase in the near term, a number of attractive technological alter- natives for thermal destruction are also emerging. These alternatives include: incineration of hazardous wastes in high-temperature industrial processes such as cement kilns and industrial boilers; incineration at sea in specially designed incineration ships or off-shore platforms; and transportable in- cineration facilities. High-temperature industrial processes The current RCRA regulations specif- ically exempt facilities that combust wastes in energy-producing operations from complying with RCRA mandates. Thus, while incinerators burning a com- bustible hazardous waste would be re- quired to achieve 99.99% DRE and the other emissions limits, a cement kiln, or industrial boiler co-firing the same waste as a fuel supplement would not be sub- jected to the RCRA emission controls. This obviously provides a considerab1e incentive to industry to employ such pro- cesses to destroy certain hazardous waste streams and to recover their energy val- ues where these wastes are compatible with their facilities. In fact, according to an EPA draft report, an-estimated 20 mil- lion metric tons of wastes per year that may otherwise have been classified as hazardous due to their characteristics are now burned as fuel or combusted with fuel in industrial energy-producing oper- ations. Cement kilns Cement kilns are particularly well- suited for -cofiring of hazardous waste. These kilns typically operate at tempera- tures and gaseous residence times in excess of those provided in high-efficien- cy hazardous waste incinerators. Lime kilns have also been considered for waste cofiring, but no known trial tests have been cond'ucted. Several cement plants in the US and_ abroad have experimented in the past with wastes as fuel sources. Most of this work, however, has not been documented. rl The trials involved waste oils and spent nonhalogenated solvents. those which have been documented are summarized in a. recent EPA study which examines the feasibility 'of waste fuel use in cement kilns. · Between March 1974 and January 1976, the St. Lawrence Cement Compa- ny in Mississauga, Ontario, conducted a series of experiments involving metal- contaminated waste oils, chlorinated or- ganic liquids (aliphatics and aromatics), and chlorinated wastes containing PCBs. The tests were conducted primarily in a 1000 ton/day (1100 metric ton/day), oil- fired wet process kiln. Waste oils were injected separately at a rate to supple- ment roughly 33% of the total kiln fuel requirement. The chlorinated organic liq- : t ' I ! I I i '\ uids and PCBs were fired at a maximum fuel replacement level of 12%. During all tests, none of the stable high-molecular weight compounds present in the waste fuels, including PCBs, were detected in the stack emissions. Similar tests have since · been con- ducted at Peerless Cement in Detroit, Michigan, on PCB oils and on four differ- ent chlorinated wastes at the Stora Vilca Cement Factory near Stockholm, Swed- en. The tests on the whole confirmed that essentially complete destruction of waste feeds was achieved. These studies indicate that waste fuel can be used to supplement as much as an average 15% of the process fuel require• ·ment. At chlorine addition rates below 0. 7% of the total fuel feed, no problems were encountered with kiln operations and there was no deterioration in cement clinker quality. At this waste firing rate, there is sufficient wet process kiln capaci- ty in the US to destroy nearly four times the estimated annual amount of chlori0 nated hazar1ous waste generated. Currently, a number of cement plants in the US are firing nonhalogenated haz- ardous waste and waste oils on a produc- tion basis. No known facilities are using highly chlorinated solvents or PCBs. One commercial concern attempted to gain approval to burn PCB oil on a production basis in 1980, but withdrew its permit application in face of public opposition. On a more positive note, the EPA will conduct hazardous waste cofiring tests at the San Juan Cement in Puerto Rico in August 1981. The State of California also recently investigated the state-of-the-art in PCB destruction and subsequently adopted a policy which encourages use of cement kilns for such purposes within its territory. No tests have taken place or are yet planned. While cement kiln cofiring has many . technical, environmental, and economic advantages, it appears that more time and testing will be needed to convince the public and industry of its benefits. High-t~mp industrial boi19rs Use of high-temperature industrial boilers to incinerate hazardous wastes is another alternative. EPA estimates that perhaps as much as 19 million metric tons per year of organic waste are cofired in boilers, including waste oils, spent sol- vents, pulping liquors, and petroleum re- fining by-products. The opportunity for incineration of hazardous wastes in indus- trial boilers is even greater than that cur- rently practiced. . · There are over 40,000 industrial boil- ers in the US with heat release capacities greater than IO X 106 BTU/h (2.7 X 105 kcal/h), the average capacity of liquid injection incinerators. Virtually all major industrial facilities which generate haz- ardous wastes have one or more boilers with at least this capacity. Since waste used for fuel in such units is also not specifically regulated under RCRA at this time, these operations are exempt from the incinerator performance standards. This may provide a substantial incentive to many industrial generators to cofire combustible hazardous waste into existing boilers where wastes are compats ible with boiler design and operation. Although the practice of cofiring is believed to be widespread,there is in fact little documented test data available. Most data are for PCBs. Utility boilers, of course, may burn PCB oils under the current PCB regulations. Nine test burns have been conducted or were planned in the last two years to demonstrate the 99.9% combustion effi- ciency required for PCB combustion. In May 1980, EPA and General Mo- tors Corporation sponsored a test trial of . PCB waste oil cofiring in a GM oil-fired boiler in Bay City, Michigan. The three• day test demonstrated thafa combustion efficiency in excess of 99.9% was achieved. One US chemical company fires a phe- nol production wastewater into its coal- fired boiler at 50% (on a fuel value basis) of the coal fuel feed. Exha11st gas analysis reveals 1 ppm or less phenol remained. The company calculates that it saves five million dollars per year in boiler fuel costs plus two million dollars per year by not having to incinerate the waste sepa• rately. Cofiring of hazardous waste in indus• trial boilers, however, is not without limi- tations. Not all boilers provide sufficient• ly high temperatures and gaseous resi- dence times to destroy many hazardous wastes. Also, boilers operate at variable . rates to accommodate changing steam demand. Combustion of halogenated waste may aiso increase corrosion of heat exchange surfaces. . . EPA is very interested in defining the environmental, operational, and engineer- ing limitations of cofiring hazardous wastes in industrial boilers. A recent study conducted by EPA esti• mated time/temperature regimes for a wide range of boiler designs, sizes, and basic fuels using zonal heat balance calcu- lations for typical installations. The study · results indicate: ·• Boilers with exit temperatures above 815 °C ( I 500 F) and residence times above one second are best candidates for destroying compounds for which destruc- tion data are currently available • Combustion in firetube boilers will not be adequate except for a very limited number of wastes • Combustion of most waste streams in watertube boilers is expected to be complete EPA is beginning an emissions testing program to verify these conclusions and to determine if potentially hazardous products of incomplete combustion may be produced. These data are to be used to determine which waste/boiler combinations are ac- ceptable and if regulations should be developed for boiler cofiring. Offshore and shipboard Incineration. Many people believe it is safer and less complicated to incinerate hazardous wastes at sea because of greater distance from· populated areas and a reduced or el.iminated need for acid gas scrubbing. Shipboard incineration of hazardous wastes has been employed in Europe since 1969. In 1974, 1975, and 1977, one of these vessels, the M/T Vulcanus, was used und~r permit from the EPA for silccess• ful destruction of organochlorine wastes, predominantly trichloropropane, trichlor- oethane, and dichloroethane, in the Gulf of Mexico and for the highly-toxic herbi- cide orange at a remote Pacific Ocean location. Destruction efficiencies for or• ganochlorines averaged 99.995%, while the herbicide orange w,s 99.999% de- stroyed. · While four vessels were originally equipped to incinerate wastes at sea, only two are still in service. EPA and the Mar-. itimc. Administration (MARAD) are in- vestigating how to pr~vide incentives to US industry to build and operate US flag incineration ships with the ability to burn solid residues as well as liquid wastes. All current incineration vessels are equipped to burn liquid waste only. EPA is also studying the possible use of an abandoned off-shore oil exploration platform as an incineraiion site. Esti- mated costs for such a facility are $6.6 million. A Draft Environmental Impact Statement is being prepared. Mobile system~ EPA is also involved in a program to . design, construct, and demonstrate a mo- bile incineration system. While initially intended to destroy debris, soils, and waste liquids from oil and hazardous materials spills, the system has taken on new significance with the recently-en- acted "Superfund" legislation for cleanup of abandon·ed waste disposal sites. The mobile Environmental Restoration Incin- erator Complex (ERIC) is composed of thr~e heavy-duty hig hway truck traile rs mounted with the necessary subsystems of a rotary kiln incineration system. The facility has been constructed and is now in shakedown testing at EPA's Edison, New Jersey, laboratory. Field demonstra- tion is planned for the fall of 1981. Q Timothy Oppdt, B.S., M.S .• is a civil enzinurint gradual~ of Cornell Univenfty and holds an MBA from Xavier University. He ha.J worked in hazardous wa,te reuart:h. solid wa.JU ,~search. and waur treatment for EPA since /970. September 1981 Civil Engineering-ASCE 75 r: ' t: ! : ! . 1 '. I ' '. '. f I . l.