Fuel waste

Fuels, alternative Fuels, combustion Fuels from biomass Fuels from waste Fuels, liquid Fuels, synthetic... 

V. Nast, G. Ekschele, and W. Hutchinson, "TDE Co-firing Experience in a Cyclone Boiler," Proceedings, Strategic Benefits of Biomass and Waste Fuels Conference, EPRI, Washington, D.C., 1993. 

Specific gravity is direcdy related to the bulk density of waste fuels prepared ia a variety of ways. Solid oven-dry (OD) wood, for example, has a typical bulk density of 48.1 kg/m (301b/ft ). In coarse hogged form, eg, <1.9-cm minor dimension, this bulk density declines to about24kg/m (151b/ft ). In pulverized form, at a particle size <0.16 cm, this bulk density declines to 16—19 kg/m (10—12 Ib/ft ). Similar relationships hold for municipal waste, agricultural wastes, and related fuels. 

Chemical Composition. Chemical compositional data iaclude proximate and ultimate analyses, measures of aromaticity and reactivity, elemental composition of ash, and trace metal compositions of fuel and ash. All of these characteristics impact the combustion processes associated with wastes as fuels. Table 4 presents an analysis of a variety of wood-waste fuels these energy sources have modest energy contents. 

Typically, 40—50% of the carbon atoms ia lignite are ia aromatic stmctures while 60—70% of the carbon atoms ia Illinois bituminous coal are ia aromatic stmctures (7,8). By all of these measures, waste fuels are significantly more reactive than coal, peat, and other combustible soHds. 

The chemical analysis of waste fuels also demonstrates that the wood-based fuels contain virtually no sulfur and Htde nitrogen. Unless the hog fuel contains bark from logs previously stored ia salt-water, the chlorine content is very modest to nonmeasurable. 

Combustion characteristics of consequence include the overall mechanism of soHd waste combustion, factors governing rates of waste fuels combustion, temperatures associated with waste oxidation, and pollution-formation mechanisms. 

Fig. 3. Schematic of the sequential nature of waste fuel combustion (1). A, particle heating and drying B, soHd particle pyrolysis and C, char oxidation. A...

Table 11. Combustion Conditions for Conventional Waste Fuel Boilers ...

Formation of Airborne Emissions. Airborne emissions are formed from combustion of waste fuels as a function of certain physical and chemical reactions and mechanisms. In grate-fired systems, particulate emissions result from particles being swept through the furnace and boiler in the gaseous combustion products, and from incomplete oxidation of the soHd particles, with consequent char carryover. If pile burning is used, eg, the mass bum units employed for unprocessed MSW, typically only 20—25% of the unbumed soHds and inerts exit the combustion system as flyash. If spreader-stoker technologies are employed, between 75 and 90% of the unbumed soHds and inerts may exit the combustion system in the form of flyash. 

There has been increased interest in firing wood waste as a supplement to coal in either pulverized coal (PC) or cyclone boilers at 1—5% of heat input. This appHcation has been demonstrated by such electric utilities as Santee-Cooper, Tennessee Valley Authority, Georgia Power, Dehnarva, and Northern States Power. Cofiring wood waste with coal in higher percentages, eg, 10—15% of heat input, in PC and cyclone boilers is being carefully considered by the Electric Power Research Institute (EPRI) and Tennessee Valley Authority (TVA). This practice may have the potential to maximize the thermal efficiency of waste fuel combustion. If this practice becomes widespread, it will offer another avenue for use of fuels from waste. 

In a rotary kiln, the burner can produce both thermal and fuel NO, if the fuel contains nitrogen. Many soHd waste streams also contain nitrogen, typically as much as 20 wt %, which contributes to the fuel NO pathway. Key sources of soHd waste fuel nitrogen include plastics, nylons, dyes, and other process wastes. Nylon, for example, is 33 wt % nitrogen. 

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

Coal was the primary kiln fuel in 1989 as seen in Table 10. Energy from coal rose from 39 to 84% of the total energy required for cement production between 1972 and 1989. In the same time period, natural gas dropped to 9%, petroleum products to 1% of the total energy consumed. Waste fuels represented 5% of the energy consumed in 1989 cement production. 

Cement plants in the United States are now carehiUy monitored for compliance with Environmental Protection Agency (EPA) standards for emissions of particulates, SO, NO, and hydrocarbons. AH plants incorporate particulate collection devices such as baghouses and electrostatic precipitators (see Air POLLUTION CONTROL methods). The particulates removed from stack emissions are called cement kiln dust (CKD). It has been shown that CKD is characterized by low concentrations of metals which leach from the CKD at levels far below regulatory limits (63,64). Environmental issues continue to be of concern as the use of waste fuel in cement kilns becomes more widespread. 

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. 

An advantage of a stoker-fired furnace is its easy adaptability to firing almost any unsized solid fuels. Bark, bagasse, or refuse can normally be fired on a stoker to supplement the coal with a minimum amount of additional equipment. Thus, such supplementaiy waste fuels may be able to contribute a higher percentage of the total heat input in a stoker-fired furnace than in a PC furnace without expensive equipment modifications. 

TABLE 27-19 Solid-Waste Fuels Burned in Industrial Boilers... 

Velocity flame stoppers have been used for feeding waste fuel gas to furnace burners when the gas can become flammable due to contamination with air. They have also been used for feeding waste or depleted air streams to furnaces when the air streams can become contaminated with flammable gases (Howard 1982). It should be noted that a furnace pressure transient may render this device ineffective and consideration should be given to providing an upstream detonation flame arrester. In this arrangement a demand will only be placed on the detonation flame arrester when the velocity flame stopper fails. Therefore, detonation flame arrester maintenance should be minimal. 

In early days, the mixture supplied to the engine was often quite rich in order to ensure smooth engine operation. This, of course, wasted fuel energy through inconiplete combustion. Fleet surveys in early years showed marked improvement in the percentage of fuel that was wasted 15.5% in 1927, 7.5%... 

Multi-stage preheating, pre-calciners, kiln combustion system improvements, enhancement of internal heat transfer in kiln, kiln shell loss reduction, optimize heat transfer in clinker cooler, use of waste fuels Blended cements, cogeneration... 

Under the same conditions of low heat-flux density, poor water chemistry, and gradual scaling circumstances, FT boilers may easily lay down from 1/16 to 1/4 inch of scale (6-12 mm) or more during a 12-month period. Tubes may become bridged by scales and sludges. Again, cleaning is required and the extra costs incurred for wasted fuel can never be recovered. 

Radioactive liquids are sometimes used 2. Some waste fuel rods from the nuclear power... 

Of the 3 million tons of hazardous waste sent for combustion, about half was processed in BIFs. Boilers are normally used for energy recovery. Hazardous waste fuels provide about 50% of a boiler s fuel requirements and are normally mixed with natural gas or other fuels.21 There are around... 

Waste Electrical and Electronic Equipment (WEEE) legislation, 20 60 Waste exchanges, 21 407 Waste facilities, design of, 21 842 Waste fuel... 

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 1. Flowchart of plasma zero-waste fuel generation process...

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