Page 523 - Materials Chemistry, Second Edition

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494 Waste Management Practices: Municipal, Hazardous, and Industrial
15.6.5 OVERVIEW OF ROTARY KILN INCINERATION
The rotary kiln is one of the more popular types of incineration systems for hazardous wastes. These
devices operate under a wide range of conditions, handle a wide variety of waste types, and gener-
ate a range of different emissions. There is no single temperature that is characteristic of a rotary kiln.
The advantages of the rotary kiln include (Brunner, 1993):

● Applicability for a number of waste types (liquids, slurries, sludges, and bulk solids)
● High turbulence provides for thorough mixing of the waste charge
● Minimal preprocessing of waste
● Many types of feed mechanisms available
● Readily controlled waste residence time in the kiln
Disadvantages include:
● High initial capital costs
● Significant costs for maintenance
● Separate afterburner required for destruction of volatile components
● Damage to kiln linings due to abrasion from solids such as drums
● Damage to the rotary seals
● High particulate carryover into the afterburner
● Conditions along the length of the kiln are difficult to control
● Ash production may be significant

15.6.6 BOILERS AND INDUSTRIAL FURNACES
As mentioned above, a boiler is composed of the combustion chamber used to heat the hazardous
waste and tubes that hold a fluid (usually water) used to produce energy (e.g., steam). The regula-
tory definition of boiler requires that these two components be situated close to one another to
ensure effective energy recovery. In addition, the unit must export or use the majority of the recov-
ered energy for some beneficial purpose. Industrial furnaces are enclosed units installed within a
manufacturing facility and use thermal treatment to recover materials or energy from hazardous
waste. These units may use hazardous waste as a fuel to heat raw materials to make a commodity
(e.g., a cement kiln manufacturing cement) or the unit may recover materials from the hazardous
waste (e.g., a smelter facility which recovers silver or lead).
Not all units that meet the definition of boiler or industrial furnace are subject to the 40 CFR
Part 266, Subpart H, BIF standards. Each individual unit is evaluated against a list of possible
exemptions from the BIF requirements. For several reasons (e.g., to avoid duplicate regulation), the
U.S. EPA exempted the following units from the BIF regulations (U.S. EPA, 2002):
● Units burning used oil for energy recovery
● Units burning gas recovered from hazardous or solid waste landfills for energy recovery
● Units burning hazardous wastes that are exempted from RCRA regulation, such as house-
hold hazardous wastes
● Units burning hazardous waste produced by a conditionally exempt small quantity generator
● Coke ovens burning only K087 decanter tank tar sludge from coking operations
● Certain units engaged in precious metals recovery
● Certain smelting, melting, and refining furnaces processing hazardous waste solely for
metals recovery

15.6.7 INDUSTRIAL BOILERS
Many industrial and commercial facilities are equipped with boilers, fired by coal, number 2 heat-
ing oil, or natural gas. Boilers are high-temperature furnaces that generate heat energy from com-
bustion. Heat is transferred by means of either a boiler adjacent to the firebox or via tubes lining the