Combustion, conditions for

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

Air pollutants derived from biofuels are the result of incomplete combustion (conditions for efficient combustion of these fuels are difficult to achieve in typical household-scale stoves) and are practically the same for any type of biomass. However, the amount and the characteristics of pollutants produced during the burning of biomass fuels depend on several factors, including the composition of original fuel, combustion conditions (temperature and air flow). 

Suwanpratech and Hattapanit [104] compared the use of black rice husk ash as a filler in epoxy resins used for embedding electrical and electronic devices to the use of commercial fillers, fused silica, and crystalline silica in various weight fractions between 20% and 60%. This led to an increased mixing viscosity, thermal expansion, and water absorption, with slightly lower tensile properties, compared to conunercial silicon fillers. It was suggested that the use of different combustion conditions for the rice husk ash, to lower the carbon content, may make the results more comparable. 

The vanadium trioxide (V2O3) and vanadium tetraoxide (V2O4) compounds are typically associated with approximate unbumed carbon levels in the flyash 10 percent. This is consistent with the porphyrin structure of the vanadium in the crude oil, and in the petroleum coke. Nickel can occur as a sulfide, an oxide, or in a vanadate (e.g., nickel pyrovanadate) depending upon combustion condition. For example, r ucing conditions promote formation of sulfide compounds. Some of the conq)ounds shown (e.g., the sodium vanadate compounds) are nK>re commonly associated with oil firing than with petroleum coke firing, as a consequence of the low ash content in petroleum coke and the low... 

Note 10— The formation of NO and NO from oxidative combustion of nitrogen containing hydrocarbons is dependent on combustion conditions such as temperature and oxygen concentration. Injection of a constant solution volume, and dilution of all test specimens and standards with a common solvent, maintain consistent combustion conditions for test specimens and standards. 

Given the mechanisms and temperatures, waste combustion systems typically employ higher percentages of excess air, and typically also have lower cross-sectional and volumetric heat release rates than those associated with fossil fuels. Representative combustion conditions are shown in Table 11 for wet wood waste with 50—60% moisture total basis, municipal soHd waste, and RDF. 

Common combustion reactions and heat releases for 0.454 kg of reactant under ideal combustion conditions are as follows, where Btu represents British thermal unit ... 

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 steam balance in the plant shown in Figure 2 enables all pumps and blowers to be turbine-driven by high pressure steam from the boiler. The low pressure exhaust system is used in the reboiler of the recovery system and the condensate returns to the boiler. Although there is generally some excess power capacity in the high pressure steam for driving other equipment, eg, compressors in the carbon dioxide Hquefaction plant, all the steam produced by the boiler is condensed in the recovery system. This provides a weU-balanced plant ia which few external utiUties are required and combustion conditions can be controlled to maintain efficient operation. 

Flow fields resulting from these combustion modes were computed by means of similarity methods (Section 4.2.1) and used to provide initial conditions for numerical computations. The main conclusion was that blast waves at some distance from the charge were very similar, regardless of whether the combustion mode was detonation or strong deflagration. 

In the application of the multienergy concept, a particular vapor cloud explosion hazard is not determined primarily by the fuel-air mixture itself but rather by the environment into which it disperses. The environment constitutes the boundary conditions for the combustion process. If a release of fuel is anticipated somewhere, the explosion hazard assessment can be limited to an investigation of the environment s potential for generating blast. 

Maximum. standard brake horsepower. At any rotational speed, maximum standard brake horsepower shall be the greatest horsepower, corrected to standard conditions, that can be sustained continuously under conditions as outlined under test procedure. The unit of horsepower is 33,000 ft-lb/min or 550 ft-lb/s. Standard conditions for the purpose of internal combustion engine testing and rating is 85°F(29.4°C) and 29.38 in. of mercury (99kPa). Note these values are different from standard conditions for gas and air volume specifications. 

The flash point of an oil is the temperature at which it gives off, under specified conditions, sufficient vapor to form a flammable mixture with air. This is very different from the temperature of spontaneous combustion. The test is an empirical one and the result depends upon the instm-ment used and the prescribed conditions. For example, the flash point may be closed or open , depending on whether the test apparatus has a lid or not. As far as lubricating oils are concerned, the test is of limited significance, although it can be indicative of contamination (for example, the dilution of crankcase oil by fuel). 

Apart from the operational problems associated with closely matching the fuel and excess air ratio requirements and the ignition and combustion temperatures for any given steam demand and local atmospheric condition, the composition of the fuel, with all its variables, adds considerably to the puzzle of providing continuously nearperfect combustion. 

Combustion-generated noise is a problem in itself. However, if an acoustic wave can interact with the combustion zone, so that the heat release rate is a function of the acoustic pressure, q = f p ), then Equation 5.1.14 describes a forced oscillator, whose amplitude can potentially reach a high value. The condition for positive feedback was first stated by Rayleigh [23] ... 

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