Multiple-Hearth Incinerators

A multiple-hearth incinerator consists of several hearths in a vertical cyhndrical furnace. The dewatered sludge is added to the top hearth and is slowly pushed through the incinerator, dropping by gravity to the next lower layer until it finally reaches the bottom layer. The top layer is used for diying the sludge with the hot gases from the... 

There are four basic types of incinerators used in wastewater treatment plants. They are the multiple hearth incinerator, the fluid bed incinerator, the electric furnace, and the cyclonic furnace. Each system has it s own distinct method of incineration and while one may be more cost efficient, another may have more of an environmental impact. 

The basic configuration and features of the multiple hearth incinerator are illustrated in Figure 23. This incinerator is the most prevalent incinerator technology for the disposal of sewage sludge in the U.S. due to it s low ash discharge. Sludge cake enters the furnace at the top. The interior of the furnace is composed of a series of circular refractory hearths, which are stacked one on top... 

The multiple-hearth incinerator (Fig. 16-6) can accept sludges containing between 60 and 75% water. The operating costs run between 0.50 and 5.00 per ton of dry solids, with total costs between 8 and 14 per ton. Design information is given in reference 62. When the sludges contain more water, fluidized-bed incinerators are sometimes used. Their operating costs run between 11 and 21 per ton of dry solids and capital costs are 15/ton.6 See reference 63 for more details. All incinerators must have the proper air-pollution abatement devices attached. 

Figure 16-6 Multiple-hearth incinerator. The wet solids enter at the top of the incinerator onto the top hearth. A rake-like device plows the sludge across the top to drop holes where they descend to the hearth below. The agitation of the sludge exposes the maximum amount of surface to the hot gases, which promotes drying.

At present, two major incineration systems, multiple hearth and fluidized bed, are employed in the United States. Approximately 80% of the incinerators used in the United States are multiple hearth incinerators [179-191] ... 

The multiple-hearth incinerator (commonly called the Herreshoff furnace) is a flexible unit that has been utilized to dispose of sewage sludges, tars, solids. 

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