Homogeneous combustion

The third approach is the hybrid combustor, which was developed at Toshiba and presented in a series of publications [95-97]. The difference with the partial catalytic combustor is that only part of the fuel is added upstream of the catalyst. This fuel is nearly completely combusted over the catalyst, bringing the temperature up to approximately 8(X)-900 C. At this point the rest of the fuel is added and then combusted homogeneously. The advantages of this approach are the same as for the partial catalytic combustor. However, the problem with catalyst overheating is less pronounced here, since complete conversion of all the fuel added to the catalyst is allowed. On the other hand, the additional fuel injection downstream of the catalyst renders the system much more complex and harder... 

First Alternative. Figure 1 illustrates the first of the two alternative production processes. Here the mother Hquor from the sodium nitrate crystallization plant, normally containing about 1.5 g/L iodine as iodate, is decanted for clarification and concentration homogenization. From there the solution is spHt into two fractions. The larger fraction is fed into an absorption tower where it is contacted with SO2 obtained by sulfur combustion. In the absorption tower iodate is reduced to iodide according to the following reaction ... 

When the partial pressures of the radicals become high, their homogeneous recombination reactions become fast, the heat evolution exceeds heat losses, and the temperature rise accelerates the consumption of any remaining fuel to produce more radicals. Around the maximum temperature, recombination reactions exhaust the radical supply and the heat evolution rate may not compensate for radiation losses. Thus the final approach to thermodynamic equiUbrium by recombination of OH, H, and O, at concentrations still many times the equiUbrium value, is often observed to occur over many milliseconds after the maximum temperature is attained, especially in the products of combustion at relatively low (<2000 K) temperatures. 

The discussion of combustion fundamentals so far has focused on homogeneous systems. Heterogeneous combustion is the terminology often used to refer to the combustion of Hquids and soHds. From a technological viewpoint, combustion of Hquid hydrocarbons, mainly in sprays, and coal combustion are of greatest interest. 

Elammability Limits The minimum and maximum concentrations of combustible material in a homogeneous mixture with gaseous oxidizer that will propagate a flame. 

Catalytic reactor. The role of the catalyst was described earlier it must burn enough of the incoming fuel to generate an outlet gas temperature high enough to initiate rapid homogeneous combustion just past the catalyst exit. 

Applicability/Limitations Fluidized beds require frequent attention for maintenance and cleaning purposes. This treatment is ideal for slurries and sludges but not for bulky or viscous wastes. The waste particles should be of a certain size and be homogeneous. Wastes must have a low sodium content and a low heavy metal content. Some refractory wastes may not be fully destroyed since these units operate at low combustion temperatures (750 to 1000°C). 

Generally, at any moment of time the concentration of components within a vapor cloud is highly nonhomogeneous and fluctuates considerably. The degree of homogeneity of a fuel-air mixture largely determines whether the fuel-air mixture is able to maintain a detonative combustion process. This factor is a primary determinant of possible blast effects produced by a vapor cloud explosion upon ignition. It is, therefore, important to understand the basic mechanism of turbulent dispersion. 

A solid propellant is a mechanical (heterogeneous) or a chemical (homogeneous, or colloidal) mixture of solid-state fuel and oxidizer-rich chemicals. Specially-formed charges of solid propellant (grains) arc placed in the combustion chamber of the solid rocket motor (SRM) at a production facility. Once assembled, the engine does not require additional maintenance, making it simple, reliable and easy to use. 

F. J. Miller, J. W. Easton, A. J. Marchese, and H. D. Ross, Gravitational effects on flame spread through non-homogeneous gas layers, Proc. Combust. Inst. 29(2) 2561-2567, 2002. 

T. Vedarajan and J. Buckmaster, Edge-flames in homogeneous mixtures. Combust. Flame 114 267-273, 1998. 

Shy, S.S., Jang, R.H., and Tang, C.Y., Simulation of turbulent burning velocities using aqueous autocatalytic reactions in a near-homogeneous turbulence. Combust. Flame, 105, 54, 1996. 

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