A new generation of incinerators is required for shipboard waste disposal to enable Navy ships access to ports and bodies of water around the world without operational constraints related to environmental laws and regulations. The present practice of overboard discharge and storage/offloading will be unacceptable. Thermal destruction is considered the ultimate solution beyond the year 2000 for all types of waste.
The objectives of this project were the following: (1) apply active combustion control to the development of a compact and efficient afterburner for a solid waste incinerator and (2) explore resonant acoustics to increase throughput of a black water sludge incinerator. Both technologies were developed under SERDP project WP-34: Compact, Closed-Loop Controlled Waste Incineration.
Active control using exhaust sensors, controller, and flow/acoustic actuators in a closed loop achieves efficient and controlled mixing/afterburning of starved-air pyrolysis products in acoustically stabilized air vortices. This process was explored in sub-scale, closed-loop tests to gain a physical understanding of the control process and in open-loop full-scale tests to increase throughput and reduce emission of an off-the-shelf marine incinerator. The performance of the new compact, actively controlled incinerator was compared with alternative disposal options (both current and other possible technologies) and evaluated for potential application to the Navy plasma arc waste destruction system.
Resonant acoustics achieve enhanced burning rates of solid beds and liquid sprays through enhanced heat and mass transfer and droplet breakup. This process was explored in laboratory tests to enhance the combustion of simulated solid wastes and in full-scale tests to increase the throughput of a full-scale mock-up of an existing Navy blackwater sludge incinerator. These tests were performed without anafterburner.
A new, open-loop controlled afterburner was tested at full scale (680kW) with cold ethylene and nitrogen. Extremely low emissions for carbon monoxide (CO) (<35 ppm) and nitrogen oxide (NOx) (<30 ppm) were achieved at only 46 msec residence time, which corresponds to a very compact system. Subsequently, the afterburner was evaluated with hot, sooty pyrolysis gases. No visible emissions remained, and the CO levels were as low as 32 ppm, and NOx levels were approximately 35 ppm. Finally, the afterburner was integrated with the Golar 500 marine incinerator. Although the BTU throughput was increased by a factor of 3.2 over the off-the-shelf Golar, the CO emission for the integrated system was decreased by an order of magnitude to 8 ppm. The afterburner performance was improved further in subscale tests using real-time, closed-loop control with diode laser sensors and a controller. This project was completed in FY 1998.
Successful shipboard demonstration of a compact incinerator with real-time exhaust monitoring for active combustion control represents a significant step towards assured waste incineration and can be the basis for next generation incinerators. The compact-incinerator technology will be essential for the development of environmentally sound ships. The closed-loop active control of the incineration process will, for the first time, assure proper incineration during design and off-design operation. Successful demonstration of the assured waste incineration on-board ships will result in significant cost savings by avoiding waste storage, off-loading and on-shore destruction costs, particularly in foreign countries.