Selection

The first step in incinerator selection is to record the volume, weight, and classes of waste collected for a period of at least two weeks. The survey should be checked against typical waste-production rates. The maximum daily operation can be estimated as three hours for apartment buildings; four hours for schools; six hours for commerical buildings, hotels, and other institutions; and seven hours per shift for industrial installations.

The results of the waste survey help to determine whether a continuous or batch-type incinerator should be installed. Batch-type units consist of a single combustion chamber (see Figure 10.11.1). If the batch furnace has no grate, the ash accumulation reduces the rate of burning. The batch incinerator is sized according to the weight of each type of waste per batch at the number of batches per day. The continuous incinerator consists of two chambers:

FIG. 10.11.1 Features of a domestic incinerator.

one for charge storage and the other an evacuated chamber for combustion. The charge chamber can be loaded at any time. Sizing is based on the pounds-per-hour burning rate required.

The nature and characteristics of the waste are usually summarized in a form such as that in Table 10.11.4. Most incinerator manufacturers offer standard, pre-engineered packages for waste types 0, 1, 2, 3, and 4 (see Tables 10.11.2 and 10.11.3). Waste types 5 and 6 usually require unique designs because the physical, chemical, and thermal characteristics of these wastes are variable. Type 6 waste tends to have low heating values but contains material that can cause intense combustion. Plastics and synthetic rubber decompose at high temperatures and form complex organic molecules that require auxiliary heat and high turbulence before they are fully oxidized. In extreme cases, three combustion chambers are necessary; operators must recycle flue gases from the secondary combustion chamber back into the primary chamber to complete the combustion process.

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