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Wastewater Treatment Operations
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
The multiple hearth furnace consists of a circular steel shell surrounding a number of hearths. Scrappers (rabble arms) are connected to a central rotating shaft. Units range from 4.5 to 21.5 ft in diameter and have from four to 11 hearths. In operation, dewatered sludge solids are placed on the outer edge of the top hearth. The rotating rabble arms move them slowly to the center of the hearth. At the center of the hearth, the solids fall through ports to the second level. The process is repeated in the opposite direction. Hot gases generated by burning on lower hearths dry solids. The dry solids pass to the lower hearths. The high temperature on the lower hearths ignites the solids. Burning continues to completion. Ash materials discharge to lower cooling hearths where they are discharged for disposal. Air flowing inside the center column and rabble arms continuously cools internal equipment.
Sludge Disposal
Published in Syed R. Qasim, Wastewater Treatment Plants, 2017
Incineration involves drying of sludge cake, followed by complete combustion of organic matter. A minimum temperature of 700°C is needed to deodorize the stack emissions. Excess air 50–100 percent over the stoichiometric air requirement is necessary. Natural gas or fuel oil is provided as an auxiliary fuel for ignition and to maintain the proper temperature. Often, sludge is incinerated with municipal solid waste and other residues. Two major incineration systems are the multiple-hearth furnace and the fluidized-bed reactor. The multiple-hearth furnace contains several hearths arranged in a vertical stack. Sludge cake enters the top and proceeds downward through the furnace from hearth to hearth. The fluidized-bed incinerator utilizes a hot sand reservoir in which hot air is blown from below to expand and fluidize the bed. Air pollution control equipment is needed in both cases to clean the emission. A discussion of sludge incineration may be found in Refs. 4 and 5.
Types of Incinerators
Published in Frank R. Spellman, Incinerating Biosolids, 2020
With each type of furnace there are disadvantages to their use. The multiple-hearth furnace, for example, requires extensive maintenance and preventive maintenance on rabble arm assemblies, hearth refractories, and ancillary equipment (i.e., fuel and air systems). The MHF requires several hours to cool to ambient temperature. When the furnace is heated too quickly, the refractories can be damaged.
Toward an on-line characterization of kaolin calcination process using short-wave infrared spectroscopy
Published in Mineral Processing and Extractive Metallurgy Review, 2018
A. Guatame-García, M. Buxton, F. Deon, C. Lievens, C. Hecker
The present study raises the possibility of using SWIR spectroscopy as a technique for the monitoring and control of calcined kaolin process. The results presented in this work, offer the criteria needed to refine the Kx and 1900D parameters and transform them into a tool capable of quantifying the amount of soluble Al2O3. For this, specific Kx and 1900D thresholds that comply with the optimum soluble Al2O3 values must be determined. Besides, the conditions for the implementation of an on-line analysis system should also be considered. In a kaolin processing plant, the calcination is performed in a Multiple Hearth Furnace, in which the temperature increases from hearth to hearth. The on-line spectral analysis would ideally be implemented by taking measurements of the feed for the calciner and at every hearth to track the evolution of the kaolin transformation sequence and establish the optimum point for the desired product.