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Show EXTERNAL ATOMIZER In this case, a special external atomizer was developed. This design contains no restrictions to the liquid which would cause blockage. It does allow a high velocity steam flow at the edge of the liquid to cause a shearing of the liquid. These steam injection points are designed to cause both a radial and tangential shearing action. The high velocity jets also create an internal recirculation due to the low pressure zone created at the center of the nozzle. This provides intimate mixing of the steam with the liquid. High steam velocities also entrain combustion air and gases with the liquid as atomization takes place insuring intimate contact of air with the droplets. With the large opening of the pipe, the liquid enters at very low velocities ( < 1 fps). This also reduces the pressure head required by the pump thereby eliminating a maintenance and replacement problem on pump parts. Droplet size with this design is not as fine as that provided by internal mix nozzles. (Fig. 6) However, combustor designs for this type of waste are sized to provide the extra residence time needed to insure complete combustion. The external nozzle design also requires a constant flow of atomizing fluid throughout the entire turndown range of the system. This means a higher atomizing rate at low fire rates. This disadvantage is offset by the ability to burn this low grade material without the constant nozzle maintenance typical of the internal mix with high viscosity materials. (4) APPLICATIONS In many plants, waste fuels are being generated which can be used within the plant in fired equipment and replace purchased fossil fuels. Systems are in operation today with combination firing of waste fuels and fossil fuels. Some of these wastes may be transported by waste disposal contractors to reprocessing operations. Others may be purchased by cement kiln operations, and yet others may be supplied to commercial incineration operations. If the waste is not of a hazardous nature (listed in App. VIII RCRA 49 CFR Part 264), then consideration should be given to its use in fired equipment (boilers, process heaters, dryers, Dowtherm heaters, etc.). If it is hazardous as designated by RCRA, a small percentage of this waste may be combined with fossil fuels (provided they are miscible and non-reactive) and still not fall within RCRA. Utilizing a high percentage of the waste as the fired fuel may require that a full-blown RCRA permit will be needed before it can be considered for use. Regulations are being modified today to prevent the use of some of the App. VIII materials in boilers as a sole source fuel. 337 Performance tests are being conducted to determine the ability to reach 99.99% ORE of the POHCs. (5) However, in units other than incinerators where cold surfaces are exposed to the flame, there is a possibility of a high level of Products of Incomplete Combustion (PICs) being formed. In these cases, trial burns will be required to insure proper operation of the system. Wastes have been fired in high intensity combustors in both fired process heaters and boilers and have provided the 99.99% ORE with very little of any PIC formation. This is due to the turbulence and temperature generated within the combustor prior to any heat transfer taking place. Before a system can be converted to waste fuel firing, it is important to review the adequacy of the burner system and the nozzle design. These are critical to reaching the desired operation. (6) REFERENCES (1) Resource Conservation and Recovery Act, Standards for Owners and Operators of Waste Facilities: Incinerators, 40 CFR 264, RCRA 3004, Federal Register, Vol. 47, No. 122, Jan. 25, 1981, Amended 1984. (2) Santoleri, J.J., "Energy Recovery - A By-Product of Hazardous Waste Incineration Systems," 15th Mid-Atlantic Industrial Waste Conference, Bucknell Univ.,June, 1983. (3) Santoleri, N.J., "Design and Operating Problems of Hazardous Waste Incinerators," AIChE, Environmental Progress., Nov., 1985. (4) Santoleri, J.J., "Spray Nozzle Selection, II Chemical Engineering Progress, Sept., 1974. (5) Olexsey, R.A., Huffman, G.L., and Evans, G.M., "Emission and Control of By-Products from Hazardous Waste Combustion Processes". (6) Santoleri, J.J., "99.99% Destruction and Removal Efficiency of Hazardous Wastes - Problems with Burner/Boiler Designs," A.S.M.E. ETCE Conference, New Orleans, La., March, 1986. |
