Oxidation Fuel Combustion

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. 2. Overall schematic of solid fuel combustion (1). Reaction sequence is A, heating and drying B, solid particle pyrolysis C, oxidation and D, post-combustion. In the oxidation sequence, left and center comprise the gas-phase region, tight is the gas—solids region. Noncondensible volatiles include CO, CO2, CH4, NH, H2O condensible volatiles are C-6—C-20 compounds oxidation products are CO2, H2O, O2, N2, NO, gaseous organic compounds are CO, hydrocarbons, and polyaromatic hydrocarbons (PAHs) and particulates are inerts, condensation products, and solid carbon products.

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...

Exhaust emissions of CO, unbumed hydrocarbons, and nitrogen oxides reflect combustion conditions rather than fuel properties. The only fuel component that degrades exhaust is sulfur the SO2 concentrations ia emissions are directly proportional to the content of bound sulfur ia the fuel. Sulfur concentrations ia fuel are determined by cmde type and desulfurization processes. Specifications for aircraft fuels impose limits of 3000 —4000 ppm total sulfur but the average is half of these values. Sulfur content ia heavier fuels is determined by legal limits on stack emissions. 

The United States generates about 20 million metric tons of nitrogen oxides per year, about 40% of which is emitted from mobile sources. Of the 11 million to 12 million metric tons of nitrogen oxides that originate from stationary sources, about 30% is the result of fuel combustion in large industrial furnaces and 70% is from electric utility furnaces. 

Combustion is the rapid exothermic oxidation of combustible elements in fuel. Incineration is complete combustion. Classical pyrolysis is the destructive distillation, reduction, or thermal cracking and condensation of organic matter under heat and/or pressure in the absence of oxygen. Partial pyrolysis, or starved-air combustion, is incomplete combustion and occurs when insufficient oxygen is provided to satisfy the combustion requirements. The basic elements of each process are shown on Figure 27. Combustion of wastewater solids, a two-step process, involves drying followed by burning. 

Nitration results from fuel combustion in engines. The products formed are highly acidic and they may leave deposits in combustion areas. Nitration will accelerate oil oxidation. Infrared analysis is used to detect and measure nitration products. 

R.D. Gould, Combustion Instability of Solid Propellants Effect of Oxidizer Particle Size, Oxidizer/Fuel Ratio and Addition of Titanium Dioxide to Plastic Pro pell ants , Rept No RPE-TR-68/1, Westcott (Engl)... 

When these metal additives are delivered to the furnace, in whatever form suitable, they become oxides. In this active form, they exert a catalytic effect on the fuel combustion process. 

Nitrogen Dioxide (NO2) Is a major pollutant originating from natural and man-made sources. It has been estimated that a total of about 150 million tons of NOx are emitted to the atmosphere each year, of which about 50% results from man-made sources (21). In urban areas, man-made emissions dominate, producing elevated ambient levels. Worldwide, fossil-fuel combustion accounts for about 75% of man-made NOx emissions, which Is divided equally between stationary sources, such as power plants, and mobile sources. These high temperature combustion processes emit the primary pollutant nitric oxide (NO), which Is subsequently transformed to the secondary pollutant NO2 through photochemical oxidation. 

I apply these computational methods to various aspects of the Earth system, including the responses of ocean and atmosphere to the combustion of fossil fuels, the influence of biological activity on the variation of seawater composition between ocean basins, the oxidation-reduction balance of the deep sea, perturbations of the climate system and their effect on surface temperatures, carbon isotopes and the influence of fossil fuel combustion, the effect of evaporation on the composition of seawater, and diagenesis in carbonate sediments. These applications have not been fully developed as research studies rather, they are presented as potentially interesting applications of the computational methods. 

Similarly, in the development of solid oxide fuel cells (SOFCs), it is well recognized that the microstructures of the component layers of the fuel cells have a tremendous influence on the properties of the components and on the performance of the fuel cells, beyond the influence of the component material compositions alone. For example, large electrochemically active surface areas are required to obtain a high performance from fuel cell electrodes, while a dense, defect-free electrolyte layer is needed to achieve high efficiency of fuel utilization and to prevent crossover and combustion of fuel. 

Bansal NP and Zhong Z. Combustion synthesis of Sm0 5Sr0 5Co03 x and Lao 6Sr04CoO3 x nanopowders for solid oxide fuel cell cathodes. J. Power Sources 2006 158 148-153. 

Liu Y and Liu M. Porous electrodes for low-temperature solid oxide fuel cells fabricated by a combustion spray process. J. Am. Ceram. Soc. 2004 87 2139-2142. 

Partial oxidation is based on extreme rich fuel combustion (low air/fuel ratios). The process is highly exothermal and can be performed in both a catalytic and a noncatalytic manner. If a catalytic system is used, the reformer can be operated at a much lower temperature and the heat can be supplied directly into the catalyst bed. The advantage with this process is that it is rather insensitive to contaminants and that it is rather independent of fuel. The biggest drawback is the risk for carbon... 

---