Staged combustion

The role of plastics in municipal solid waste combustion is discussed, and in particular, their fuel characteristics. Details are given of a state-of-art municipal solid waste combustor and the effects of plastics on the different combustion stages. In addition, the contribution of plastics to the total output spread over the various emission paths of solids, liquids and gases, is also assessed. 

COPE [Claus Oxygen-based Process Expansion] A modification of the Claus process, which improves the recovery of the sulfur. The combustion stage uses oxygen instead of air. Introduced in 1985 and now licensed by Air Products Chemicals and Goar, Allison Associates. In 1990, six units were operating in the United States. 

Air-sampling detector Actively and continuously samples the air from a protected space and is able to sense the pre-combustion stages of incipient fire. 

Iron is the chemical element with the highest binding energy in the nucleus. Consequently, the thermonuclear fusion process cannot proceed beyond this point. The successive combustion stages (hydrogen, helium, carbon, neon. 

The control of NO from stationary sources includes techniques of modification of the combustion stage (primary measures) and treatment of the effluent gases (secondary measures). The use oflow-temperature NO,.burners, over fire air (OFA), fiue gas recirculation, fuel reburning, staged combustion and water or steam injection are examples of primary measures they are preliminarily attempted, extensively applied and guarantee NO reduction levels of the order of 50% and more. However, they typically do not fit the most stringent emission standards so that secondary measures or flue gas treatment methods must also be applied. 

The determination of deviations in isotopic ratios requires very precise measurements. The combustion stage involved is usually carried out immediately before injection into the mass spectrometer. Some instruments have been developed that include a gas chromatograph in line with a tubular combustion oven (containing copper oxide at 800 C) and a low-resolution magnetic sector instrument. The mass spectrometer is equipped with a multicollector that allows recording at each individual mass (see Fig. 16.24). 

The results enable us to deduce a general mechanism for the reactions underlying (a) the change which often occurs in the nature of the effect of halogen compounds in going from one combustion stage to another and (b) the relative differences in the effectiveness of different halogen compounds. 

Several issues need to be considered in relation to control of the post-combustion stage of a combustor ... 

Combustion of fuel focuses on the production of CO2 and H2O, but a small amount of N2 also oxidizes to form various nitrogen oxides, NOx, that are pollutants. Increasingly stringent federal and local regulations for the permitted NO emmissions in flue gas discharge have led to various technologies for NOx reduction. A combination of combustion staging, premix combustion, and recirculation make it possible to achieve low NQc levels. 

However, an attendant cost of pressure operation throughout the process is nitric oxide yields of only 90-95% from the ammonia combustion stage compared to yields of 97-98% at atmospheric pressure. For this reason atmospheric pressure processes are still viable and continue to operate. To obtain the greater ammonia oxidation efficiencies possible at near atmospheric pressure and to retain the more efficient absorption at elevated pressures many European producers use split-pressure processes [46]. This combination is particularly valuable when ammonia costs are high. However, the ammonia saving has to be balanced against capital costs of split-pressure plants 1.5 to 2 times that of the other two alternatives because of the need for compressors constructed from exotic metals. 

The basic concept of a thermal process using pyrolysis and combustion stages coupled by heat pipes is workable and eliminates the need to recycle large amounts of sand. 

FIGURE 9 Biomass-C partitioning in different combustion stages of natural tires with an average combustion efficiency of 80wt-%. Values for gas and tar are ased on estimations. (Fearnside et al, 1993 Kuhlbusch et al, 1996 Laursen et al., 1992 Lobert and Warnatz, 1993 Sinioneit, 1999.)... 

The design of the regeneration stage in an adiabatic fixed bed requires to solve the heat balance in the coke combustion stage, eq. (13), which takes into accoimt the heat accumulation at the wall of the reactor... 

Improvements in the reduction of flammability of polymers with low clay contents and better processability have been reported, in addition to reductions in the concentration of toxic vapors produced in the combustion stage [116-120]. In connection to their flame-retardant properties, exfoliated nanocomposites based on PP [121, 122, 115, 123], PS [115, 123, 124], poly(ethylene-vinyl acetate) [125, 126], styrene-butadiene rubber [127], PMMA [128], polyesters... 

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