Wood, combustion process

U. Wieser and C. K.. Gaegauf, Nanoparticle emissions of wood combustion processes, June 2000, Sevilla, 1st World Conference and Exhibition on Biomass for Energy and Industry,. 

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. 

With a solid fuel, such as coal or wood, a series of steps are involved in combustion. These steps occur in a definite order, and the combustion device must be designed with these steps in mind. Figure 6-6 shows what happens to a typical solid fuel during the combustion process. 

Energy recovery from packaging waste is discussed, with particular reference to the co-combustion of mixed plastics with other conventional fuels such as wood, coal and peat. Experimental work is described in which a project was established to evaluate the possibility of energy recovery from a circulating fluidised bed boiler using packaging from different sources as fuel. The role of sulphur in the formation of PCDD/F in the combustion process was also studied. 

Carbon monoxide (CO) is generated in incomplete combustion processes. In households the main sources are all kinds of fuel burners (fuel oil, wood, natural gas, coal etc.) and automotive exhaust gas. Carbon monoxide is an odorless and invisible gas, and, due to its affinity to hemoglobin, which is higher than that of oxygen, it reduces the blood s capacity to carry oxygen. Hence it is toxic, especially for unborn and small children as well as for the elderly or people with heart problems or anemia. Even small amounts of CO can be harmful. Tab. 5.6 gives an overview of the relation between CO concentration and the corresponding symptoms of intoxication. 

Thermal reactions leading to the PCDD/F emissions are connected with technological and domestic combustion. PCDD/Fs were found in the emissions of the various combustion processes independently from the fuel municipal and hazardous waste incinerators, power plants with fossil fuels, automobile exhaust, private heating and fire places, wood and forest fires,... 

The overfired batch conversion process, as well as the combustion process, of wood fuels is shown to be extremely dynamic. The dynamic ranges for the air factor of the conversion system is 10 1 and for the stoichiometric coefficients is CHs.iOiCHoOo during a batch for a constant volume flux of primary air. The dynamics of the stoichiometry indicates the dynamics of the molecular composition of the conversion gas during the course of a run. From the stoichiometry it is possible to conclude that... 

The objective of AxelTs [11] experimental study is twofold (1) to develop methods to study the combustion process of a packed-bed of biomass (2) to study the effect of mass flow of air on the combustion process in different conditions with respect to fuel particle size, density, and shape. The results are planned to be applied to computer simulations of packed-bed combustion of wood fuels as well as design data for construction of PBC systems. 

Combustion processes are fast and exothermic reactions that proceed by free-radical chain reactions. Combustion processes release large amounts of energy, and they have many applications in the production of power and heat and in incineration. These processes combine many of the complexities of the previous chapters complex kinetics, mass transfer control, and large temperature variations. They also frequently involve multiple phases because the oxidant is usually air while fuels are frequently liquids or solids such as coal, wood, and oil drops. 

Biomass differs from conventional fossil fuels in the variability of fuel characteristics, higher moisture contents, and low nitrogen and sulfur contents of biomass fuels. The moisture content of biomass has a large influence on the combustion process and on the resulting efficiencies due to the lower combustion temperatures. It has been estimated that the adiabatic flame temperature of green wood is approximately 1000°C, while it is 1350°C for dry wood [41]. The chemical exergies for wood depend heavily on the type of wood used, but certain estimates can be obtained in the literature [42]. The thermodynamic efficiency of wood combustors can then be computed using the methods described in Chapter 9. 

CDDs have been measured in all environmental media including ambient air, surface water, groundwater, soil, and sediment. While the manufacture and use of chlorinated compounds, such as chlorophenols and chlorinated phenoxy herbicides, were important sources of CDDs to the environment in the past, the restricted manufacture of many of these compounds has substantially reduced their current contribution to environmental releases. It is now believed that incineration/combustion processes are the most important sources of CDDs to the environment (Zook and Rappe 1994). Important incineration/combustion sources include medical waste, municipal solid waste, hazardous waste, and sewage sludge incineration industrial coal, oil, and wood burning secondary metal smelting, cement kilns, diesel fuel combustion, and residential oil and wood burning (Clement et al. 1985 Thoma 1988 Zook and Rappe 1994). 

Nitro-polycyclic aromatic hydrocarbons, referred to as nitro-aromatic compounds hereafter, constitute one of the most troubling classes of environmental pollutants. They are derivatives of polycyclic aromatic hydrocarbons (PAHs) that contain two or more fused aromatic rings made of carbon and hydrogen atoms and at least one nitro group (Fig. 10.1). Concern about these compounds arises partly from their ubiquity nitro-aromatic compounds are released to the environment directly from a variety of incomplete combustion processes [1] and are also formed in situ by atmospheric reactions of PAHs [2]. Nitro-aromatic compounds have been found in grilled food in diesel, gasoline, and wood-smoke emissions and are commonly found in atmospheric particulate matter, natural waters, and sediment [3-8],... 

A number of combustion and chemical production processes contribute to environmental concentrations of PCDD/F. Sources that have traditionally caused the greatest concern include municipal waste incinerators, hospital waste incinerators, bleached chemical wood pulp and paper mills, motor vehicles and wood combustion. We have attempted to represent the most recent data available on PCDD/F emissions from these sources. It should be remembered that the list presented here is by no means exhaustive. Potential sources of TCDD not discussed in the following paragraphs include discharges from metal processing and treatment plants, copper smelting plants and pentachlorophenol production. 

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