The PYROKILN THERMAL ENCAPSULATION process is designed to improve conventional rotary kiln incineration of hazardous waste. The process introduces inorganic additives (fluxing agents) with the waste to promote incipient slagging or thermal encapsulating reactions near the kiln discharge. The thermal encapsulation is augmented using other additives in either the kiln or in the air pollution control (APC) baghouse to stabilize the metals in the fly ash. The process is designed to (1) immobilize the metals remaining in the kiln ash, (2) produce an easily handled nodular form of ash, and (3) stabilize metals in the fly ash, while avoiding the problems normally experienced with higher temperature "slagging kiln" operations.
The basis of this process is thermal encapsulation. Thermal encapsulation traps metals in a controlled melting process operating in the temperature range between slagging and nonslagging modes, producing ash nodules that are 0.25- to 0.75-inch in diameter.
The figure below illustrates the process. Wastes containing organic and metallic contaminants are incinerated in a rotary kiln. Metals (in particular, those with high melting points) are trapped in the bottom ash from the kiln through the use of fluxing agents that promote agglomeration with controlled nodulizing.
The PYROKILN THERMAL ENCAPSULATION process may reduce leaching of metals to levels below EPA toxicity characteristic leaching procedure (TCLP) limits for metals. Metals with low melting and vaporization temperatures, such as arsenic, lead, and zinc, are expected to partially volatilize, partitioning between the bottom ash and the fly ash. Metals concentrated in the fly ash may be stabilized, if necessary, by adding reagents to the kiln and to the APC system to reduce leaching to below TCLP limits. This process may also reduce the total dust load to the APC system and the amount of particulate emissions from the stack.
The use of fluxing reagents is a key element in this technology. The fluxing agents are introduced into the kiln in the proper amount and type to lower the ash's softening temperature. Proper kiln design is required to allow the kiln outlet to function as an ash agglomerator. Good temperature control is required to keep the agglomerates at the correct particle size, yielding the desired 0.25- to 0.75-inch nodules. By producing nodules, rather than a molten slag, the process is expected to prevent operating problems such as ash quenching, overheating, and premature refractory failure. The process should also simplify cooling, handling, and conveying of the ash.
The controlled nodulizing process should immobilize metals with high boiling points. Lead, zinc, and other metals with lower volatilization temperatures tend to exit the kiln as fine fumes. Reagents can be injected into the kiln, the APC devices, or a final solids mixer to aid in the collection of these metals from the gas stream.
The technology is intended for soils and sludges contaminated with organics and metals. As with other rotary kiln systems, the process is expected to destroy a broad range of organic species, including halogenated and nonhalogenated organics and petroleum products. Svedala Industries, Inc., claims that metals that may be encapsulated or stabilized include antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, nickel, selenium, silver, thallium, and zinc.
This technology was accepted into the SITE Emerging Technology Program in March 1990. A final report has been prepared, and a technical paper summarizing the project was presented in 1994 at the Air and Waste Management Association 87th Annual Meeting and Exhibition in Cincinnati, Ohio. The final report was published in the July 1995 issue of the Journal of the Air and Waste Management Association.
A synthetic soil matrix was created for the batch rotary kiln tests. Feed preparation was a key element in nodule production. These tests yielded nodules with appropriate crush strength. Test results showed a decrease in TCLP metal leachate levels with increasing crush strength.
An analytical method involving microwave-aided digestion was used to evaluate samples produced in a second batch kiln test program. This method provided excellent, consistent results, indicating leachability below TCLP limits.
EPA PROJECT MANAGER:
Marta K. Richards
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7692
Fax: 513-569-7676
TECHNOLOGY DEVELOPER CONTACTS:
Jim Kidd
Svedala Industries, Inc.
20965 Crossroads Circle
Waukesha, WI 53186
414-798-6341
Fax: 414-798-6211
Glenn Heian
Svedala Industries, Inc.
Process Research and Test Center
9180 Fifth Avenue
Oak Creek, WI 53154
414-762-1190
Fax: 414-764-3443