Hazardous Waste Incineration

APTB researchers have extensive experience in examining fundamental phenomena associated with hazardous waste incineration. This research program was conducted in APTB's research laboratory on bench- and pilot-scale equipment. Initially, surrogate hazardous wastes consisting of reagent grade chemicals were used in performing tests. In 1990, APTB obtained a RCRA Research, Development, and Demonstration (RD&D) permit which allows testing to be performed on actual RCRA wastes. All of the research combustors have exhaust manifolds connected to the flue gas cleaning system, enabling unique research and development combustion studies to be performed using the individual research combustors. Thus, no pollutants are emitted to the atmosphere. Descriptions of the individual research combustors are included in the following paragraphs.

Commercial Package Boiler

This test facility consists of a commercial North American Scotch-Marine type boiler as the primary component. The boiler's burner is capable of firing gas or any grade of fuel oil, singly or in combination, and is rated at 0.73 MW (2,500,000 BTU/hr).

Studies performed on the commercial package boiler have included examination of the effect of transient boiler operating conditions on destruction and removal efficiency (DRE) of chlorinated waste, development of an artificial intelligence-based NO_x control system, and characterization of hazardous air pollutants from the combustion of heavy oils in a firetube boiler. Studies of particulate matter emissions from the combustion of heavy fuel oils are also being conducted on the boiler.

Package Boiler Simulator

The precombustion chamber burner/package boiler simulator is a staged combustion technology capable of achieving NO_x emissions of less than 0.1 lb (as NO₂)/1,000,000 BTU (0.043 ng/J or approximately 90 ppm NO_x), even with high nitrogen content fuels. The pilot-scale experimental facility consists of a vertical low NO_x precombustion chamber burner and a horizontal watertube package boiler simulator. A conventional high-swirl burner with primary air and fuel injection systems provides substoichiometric primary air and fuel/waste to the precombustion chamber (combustor region 1). The sections have a thick refractory wall lining to minimize heat loss and maintain high (near adiabatic) temperatures that promote conversion of fuel nitrogen to N₂ under fuel-rich stoichiometries. A water-cooled transition section (0.25m inside diameter) cools the combustion gas before secondary air addition to minimize thermal NO_x generation. The pilot-scale boiler simulator is rated at 0.9 MW (3,000,000 BTU/hr) thermal input. The burner transition section allows for radial addition of staged air (combustor region 2). Additionally, the boiler's front face has two ports for addition of staged (reburning) fuel at an angle of 45 degrees off axis and six axial ports for the addition of axial reburn air. This design allows for reburning application from the boiler front face with aerodynamic separation of the fuel-lean (combustor region 2), fuel-rich (combustor region 3), and fuel-lean (combustor region 4) zones in the boiler.

Studies performed on the package boiler simulator have included: (1) Multistaged Burner Evaluation: Surrogate Waste in Fuel Oil; and (2) Dinoseb Destruction.

Rainbow Horizontal Tunnel Combustor

Several experimental programs examining different issues of waste incineration have been conducted and continue to be conducted using the 83 kW (280,000 BTU/hr) horizontal tunnel combustor. This bench-scale combustor is a refractory-lined cylinder with a quartz window for flame observation and multiple ports for in-flame and post-flame sampling. A movable-block International Flame Research Foundation (IFRF) type variable swirl burner with interchangeable gaseous and liquid fuel nozzles is capable of providing near-burner-zone aerodynamic simulation of various flame types.

Studies performed on the tunnel combustor have included: (1) Droplet Trajectory and Incineration in Turbulent Diffusion Flames; (2) Chlorine/NO_x Interactions; (3) Metal Aerosol Formation; and (4) Combustion of Hydrocarb Fuel.

Rotary Kiln Incinerator Simulator

The EPA rotary kiln incinerator simulator is a 73 kW (250,000 BTU/hr) pilot-scale simulator that exhibits the salient features of full-scale units with thermal ratings which are 20 to 40 times larger. The simulator matches the volumetric heat release, gas-phase residence time, and temperature profile of many full-scale units, and yet is flexible enough to allow parametric testing.

Research projects performed using the rotary kiln include: (1) Examination of Phenomena Related to Secondary Combustion Chambers; (2) Incineration of Microelectronic Industry Waste; and (3) Development of Target Analyte List for HWI Risk Assessment Activities.

Two-Staged Fluidized Bed Combustor

APTB has conducted research to study hazardous waste incineration with trace metal capture and acid gas control in fluidized-bed combustion (FBC) systems. These systems provide unique capabilities for solving incineration and metal capture problems. Initial research focused on determining the feasibility of capturing trace metals in a bed material that would retain the metals in a landfill-suitable product.

The two-stage FBC system was designed and built to provide two different environments, one optimized for capture conditions and one optimized for high destruction and removal efficiency (DRE). Tests were conducted using a surrogate waste mixture of paint primer containing lead (Pb) and chromium (Cr) suspended in mineral spirits. This surrogate waste was burned at 1300 °F (700 °C) in a bed of silica sand (20-100 mesh) and the bed material tested for increases in Pb and Cr content. The metal capture was less than 10% using the plain sand bed. When a small amount of fluxing material (sodium carbonate) was added to the bed, a dramatic increase in metals capture occurred. Over 90% of both Pb and Cr were held in the bed material. The resulting bed material was subjected to leachability tests and passed; thus, it is not categorized as a hazardous waste and can be disposed of by conventional methods.

Flue Gas Cleaning System

All of the previously listed combustors have exhaust manifolds connected to a dedicated flue gas cleaning system (FGCS). The FGCS consists of a 1.2 MW (4,000,000 BTU/hr) afterburner followed by a spray quench, baghouse, and wet scrubber. APTB's RCRA RD&D permit is based on the operation of the FGCS, rather than the operation of any individual research combustor. Research can be performed on the individual combustors over a wide range of operating conditions, even those considered non-standard for normal incinerator operation, without emitting the resulting pollutants into the atmosphere. The FGCS was also designed so that research can be performed on it as needed.

Office of Research & Development | National Risk Management Research Laboratory