Waste fuel incinerator

F. S. Larsen, The Thermal Treatment of Contaminated Soils and the Incineration of Waste Fuels, PhD dissertation. University of Utah, Salt Lake City, 1994. 

There are numerous misconceptions about the sources of various chemical elements in waste, particularly those that are potential acid formers when the waste is incinerated or mechanically converted and used as a refuse-derived fuel. For example, it is often mistakenly stated that the source of chlorine in waste, hence a potential source of HCl emissions, is poly(vinyl chloride). The relative contents of selected, potentially acid-forming elements in the organic portion of a sample of waste collected from various households in one U.S. East Coast city is given in Table 2 (17). In this city, a chief source of chlorine in the waste is NaCl, probably from food waste. 

Incineration with Heat Recovery Heat contained in the gases produced from the incineration of solid wastes can be recovered as steam. The low-level heat remaining in the gases after heat recoveiy can also be used to preheat the combustion air, boiler makeup water, or solid-waste fuel. 

The most important current technique for the thermal destmction of waste is incineration, where the energy required for destmction is provided by oxidation of the waste, sometimes supplemented with a fossil fuel. The major question about all thermal destmction techniques is whether products from the process—either traces of umeacted parent compound or compounds synthesized from the parent compound at high temperature— will pose a health hazard. 

A major advantage of plasma processing is that the heat input may be accomplished in an atmosphere of any desired composition and reactivity. In practice there are only a few variations of chemical strategies available for thermal processing i.e. pyrolysis, oxidation, reactions with hydrogen and water. They were already reported elsewhere [5]. The most cost effective and friendly to the environment are the approaches of plasma employing for zero-waste fuel generation or for zero-waste incineration. 

Figure 14 Incineration system flow diagram. Waste is incinerated in the presence of air and supplemental fuel the incinerator can be multiple hearth, fluidized bed, liquid injection, rotary kiln, or other types caustic or lime scrubbers are used to remove gaseous pollutants from exhaust gases (from Ref. 11).

Incinerators that accept only liquid wastes either blend them with fuels or incinerate directly. In either case, the disposer generally pumps the contents from the container. Small containers are less desirable than the standard 200-liter drum. Incinerators that accept solid waste generally incinerate without removing the waste from the container, avoiding the hazards of opening containers. Some facilities will accept a variety of containers, including individual bottles. Others prefer to accept wastes in fiber packs, which is a combustible version of the lab pack used in landfills. 

Every engineer whose responsibilities include furnaces, fuels, incinerators or processes involving offgases is occasionally confronted with an offgas or a waste stream that needs to be incinerated. Such streams are sometimes so low in their combustible content that one cannot even be sure that they will burn in such cases, there is frequently a voice in the background requesting an immediate estimate of the amount and value of primary fuel required to incinerate the gas stream. 

The reader should also note that this equation is sensitive to the value assigned to the coefficient which represents the average heat capacity of the flue gas, in this case, 0.325. This is a function of both the temperature (7) and excess air fraction (EA) and also depends on the flue products since the heat capacities of air and CO2 are about half that of H2O. In addition, the 7.5 x 10 " term may vary slightly with the composition of the waste-fuel mixture incinerated. The overall relationship between operating temperature and composition is therefore rather complex, and its prediction not necessarily as straightforward as shown here. 

Additional releases of manganese to the environment occur from natural sources and from processes such as combustion of fossil fuel, incineration of wastes, or cement production (EPA 1985c, 1985d). Quantitative data on releases of manganese to specific environmental media are discussed below. 

The composition of the exhaust depends on the type and composition of the fuel and on combustion conditions. The main components are O2 (0-15%), CO2 (3-12%), H2O (6-18%) and N2. Typical ranges of air pollutants from the combustion of natural gas, oil and coal are shown in Table I. In addition to NOx, commonly encountered pollutants include carbon monoxide (CO), hydrocarbons or Volatile Organic Compounds (VOCs), sulfur oxides (SOx) and particulates. Municipal Solid Waste (MSW) incinerator or waste-to-energy plant exhausts may also contain acid gases (e.g., HCl, HF), dioxins, furans and trace amounts of toxic metals such as mercury, cadmium and lead. 

Firetube boilers may be directly fired with waste fuels, either liquid or gaseous. They also serve to recover heat from incinerators fired on waste fuels. 

The act does not cover radioactive waste, which falls imder the Atomic Energy Act of 1954. Later, the Uranium Mill TaiUngs Radiation Control Act of 1978 gave the EPA responsibility for cleanup of radioactive materials from inactive uranium processing sites. RCRA does not include water pollutants regulated by the Clean Water Act of 1972. Also excluded by RCRA were boiler fuel incinerators. Many... 

Other low or intermediate level wastes from reprocessing or MOX fuel production can be stored safely. There remains an area for technical development for some specific waste forms. Incineration of combustible liquid and solid waste looks promising but has yet to be demonstrated at an industrial scale. 

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