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Incineration Processes and Environmental Releases
Pages 34-70

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From page 34...
... Combustion in a furnace, producing hot gases and a bottom ash residue for disposal. Gas temperature reduction, frequently involving heat recovery via steam generation.
From page 35...
... Fugitive emissions, residual ash, and scrubber water handling are briefly discussed. WASTE STORAGE, FEED PREPARATION, AND FEEDING Table 3-1 lists the common waste storage, waste staging, feed preparation and feeding practices for municipal solid-waste, hazardous-waste, and medicalwaste incinerators.
From page 36...
... 36 Cq an C)
From page 37...
... , combustible components of organic compounds are burned off, leaving the incombustible particulate matter known as fly ash entrained in the flue gas. The incombustible portion of the waste (known as bottom ash)
From page 38...
... Considerable attention has also been given to measurement and control of key process operating conditions to allow better control of the whole combustion process. Furnace Types Table 3-2 lists the types of furnaces used for municipal solid-waste, hazardous-waste, and medical-waste incineration.
From page 39...
... Furnace Design Considerations For Municipal-Waste Incinerators The design of the furnace is critical to optimal combustion. Furnace configurations depend on what they were designed to burn.
From page 40...
... In plants built before the middle 1980s, particularly those with holes in the furnace walls, the entry of primary and secondary air is not as well controlled, and the excess-air rates required for adequate combustion can be several times the amount that would be required with a more modern design. This can result in larger volumes of flue gas to be treated for contaminant removal, and reduced efficiency of utilization of the exhaust heat.
From page 41...
... The process is used to lower nitrogen oxide formation by limiting the flame temperature and by slightly diluting the flame oxygen concentration. Care must be taken to ensure that not too much flue gas is recirculated, lest the combustion process be adversely affected.
From page 42...
... Modern municipal solid-waste incinerators in the United States are equipped for particulate, acid gas, and, in many cases, dioxin and mercury removal. These municipal solid-waste incinerators typically employ fabric filters or dry electrostatic precipitators (esp)
From page 43...
... Cement kilns and coal-fired boilers that burn waste as fuel have traditionally used either fabric filters or dry electrostatic precipitators as active control techniques. Passive controls include the neutralization of acid gases by cement materials and the recycling of cement kiln dust back into the process.
From page 44...
... Dry ESPs are less effective than fabric filters for collection of submicrometer particulate matter (0.1-1.0 ,um) but are nevertheless very effective collection devices.
From page 45...
... In a properly designed unit, the most-important monitoring and process control measures are pressure drops, liquid and gas flow rates, and liquid blowdown rate (blowdown is used to control solids buildup)
From page 46...
... Combustion-furnace designs that reduce thermal NOX include a variety of grate and furnace designs, bubbling and circulating fluidized-bed boilers, and boiler designs, especially those with automatic controls, that permit flue-gas recirculation. Combustion-process modifications that reduce NOX formation include controlling the amount of oxygen available during the combustion process, and operating within a specific temperature range.
From page 47...
... For high efficiency mercury removal, many municipal solid-waste incinerators and a smaller number of hazardous-waste and medical-waste incinerators have adopted powdered activated-carbon injection upstream of dry particle collection devices, usually fabric filters. As for dioxin removal, the effectiveness of powdered activated-carbon injection is determined by the carbon type, dosage, gas temperature, and gas-contact efficiency.
From page 48...
... . SYSTEM OPERATION Many variables that affect incinerator operation are controlled by operators, so the combustion conditions that control emission rates may be substantially affected by operator decisions.
From page 49...
... The American Society of Mechanical Engineers has developed a certification guideline for hazardous waste-incinerator operators. Monitoring and Data Collection For the most recently completed waste incinerators, particularly hazardouswaste incinerators, environmental regulations have led to extensive monitoring of key incineration process conditions, including waste feed rates; feed rates of ash, chlorine, and toxic metals (determined by sampling and analysis of the waste stream)
From page 50...
... The inorganic-ash fraction of the particulate matter consists of mineral matter and metallic species. These materials are conserved in the combustion process and leave the combustion chamber as bottom ash or fly ash.
From page 51...
... Source control of ash-producing waste constituents is an obvious method to reduce particulate emission, but it is impractical for most waste combustors. However, some incinerators and boilers burning liquid hazardous waste are able to meet particulate matter emission limits by stringent source selection alone.
From page 52...
... Mercury Heavy metals in waste are not destroyed by incineration. Metallic elements with high vapor pressures, or with compounds that have high vapor pressures, can be converted to the vapor phase in the combustion chambers and tend to condense as the flue gas is cooled.
From page 53...
... Volatile forms of Pb, such as PbCl2, might vaporize completely in the combustion process, whereas nonvolatile species, such as PbO, tend to partition to the bottom ash in the primary combustion chamber. Pb in liquid wastes fed through burners is exposed to flame temperatures and is, thus, more likely to vaporize than Pb in solid wastes.
From page 54...
... Designing and operating the primary combustion chamber to minimize fly-ash carryover. Using well-designed and properly operated APCDs.
From page 55...
... Other requirements for dioxin and furan formation include prolonged gas-residence time in the stated temperature range, the presence of carbon as gaseous PICs or particles, and the presence of chlorine as HC1, C12, or metal salt. Some types of organic compounds, such as chlorophenols and chlorobenzenes, tend to act as precursors for this type of secondary dioxin and furan formation.
From page 56...
... A number of hazardous-waste incinerators equipped with wet scrubbers might meet regulatory standards without other addon control. For cement kilns, analysis of the characteristics traditionally used to measure combustion efficiency (CO and total hydrocarbons)
From page 57...
... Trial burns of hazardous-waste incinerators are intended to establish operating permit limits as well as to measure emissions performance. To meet this purpose, trial burns are usually conducted at extreme combinations of operating conditions, such as minimum combustion temperature for organics emission testing; maximum combustion temperature for metals emission testing; minimum combustion residence time and maximum gas flow rate; maximum feedrates of ash-bearing waste, halogens, and metals; and worst-case air pollution control system operating conditions.
From page 58...
... Interim measures (principally modification of water sprays to reduce the gas temperature into the ESPs, together with modification of combustion conditions) reduced the concentrations to 37 to 1,500 ng/dscm (reductions of approximately 4-fold for 4 units, and 240-fold for the fifth)
From page 59...
... municipal-waste incineration facilities over the period 1985 to 1995 using the same EPA memorandum augmented with some additional individual test reports. Their calculations confirmed the large range of total emissions from different facilities, the importance for national emission estimates of the largest emitters, and the large effect on such estimates of reducing emission rates for the large emitters.
From page 60...
... of liquid organic waste to the secondary combustion chamber for 7 seconds. The transients did not change average process conditions, but CO spikes to 700 ppm were obtained, increasing the average CO from around 0-3 ppm to 10-15 ppm, with highly variable total hydrocarbons (barely increased from a baseline 0-8 ppm in one run, increased to 60-150 ppm in two other runs)
From page 61...
... stated that "test results indicate that levels of dioxin and furan in the flue gas entering a pollution control device are affected by different plant operating conditions if the conditions deviate sufficiently from normal operations," that furnace temperature can be used as a gross indicator of total dioxin and furan emissions, and that operating an incinerator at excess oxygen levels below about 5% may cause an increase in dioxin and furan emissions. The Quebec City mass burn incinerator (Finkelstein et al.
From page 62...
... and combustion air flow rates/distributions were the primary independent variables defining operating conditions as "good," "poor," and "very poor." Dioxins, furans, CO, total hydrocarbons, PCBs, chlorobenzenes, chlorophenols, and PAHs were measured. Multiple-regression models were developed to evaluate the effect of various continuously monitored emission and process parameters on dioxin emissions (prediction models)
From page 63...
... However, the high-temperature seals on rotary-kiln incinerators are a potential source of vapor and dust emissions peculiar to such incineration facilities; these emissions are controlled by maintaining a negative pressure in the kiln. ASH AND OTHER RESIDUES Types of Ash and Other Residues Residues generated by incinerators include bottom ash , fly ash, scrubber water, and various miscellaneous waste streams.
From page 64...
... For example, waste-to-energy plants produce blow-down water from the heat recovery boilers; some municipal solid-waste incinerators recover small quantities of condensed metals (e.g., lead alloys) from parts of their flue gas system.
From page 65...
... SUMMARY The pollutants of concern including dioxins and furans, heavy metals (in particular, cadmium, mercury, and lead) , acid gases, and particulate matter, either are formed during waste incineration or are present in the waste stream fed to the incineration facility.
From page 66...
... Mercury and its salts, for example, are volatile, so most of the mercury in the waste feed is vaporized in the combustion chamber. In the cases of lead and cadmium, the partitioning between the bottom ash and fly ash will depend on operating conditions.
From page 67...
... The committee has identified specific best practices for reducing incineration emissions primarily from municipal solid-waste incineration; see Box 3-1.
From page 68...
... CEMs for particulate matter and total mercury are under development and are in the process of being certified. Emissions from incineration facilities can be reduced by choosing advanced combustion designs and emission-control technologies for the pollutant of concern and by having well-trained and certified employees who can help to ensure that the combustor is operated to maximize combustion efficiency and that the emission control devices are operated to optimize conditions for pollutant capture or neutralization.
From page 69...
... Government agencies should gather and disseminate information on the effects on emissions and ash as a result of various operating conditions, such as furnace and downstream flue-gas temperatures, reagent types and injection rates, and air-injection adjustments. Such guidance should show how specific emissions and ash characteristics are affected by modifying these process conditions.
From page 70...
... . When it is appropriate, data should be standardized to 7% oxygen and measurements to units of dry standard cubic meters.


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