Unbumt carbon

Flue gases containing enough unbumt carbon and hydrocarbons so as to cause discoloration and usually measured by comparison with standard color charts. 

Figure 5. The changes in the level of unbumt carbon within the combustion product of char derived from coals of the oxidised series A and B.

Figure 10. The relationship between unbumt carbon within the char combustion product and the atomic O/C ratio of the parent coals.

Such correlations have important bearings on the current level of understanding regarding the mechanisms of pyrolysis devolatilisation and char formation. Furthermore, standard forms of analyses are subject to oxidation or weathering effects and this study demonstrates that correlations between levels of unbumt carbon and vitrinite reflectance (33) maybe potentially misleading unless the affects of oxidation or weathering are considered. 

Here, paraffin wax decomposes into free hydrogen and carbon. This is the luminous part of the flame. The flame is yellow due to the unbumt carbon particles. 

The quantities of flue gas produced, flue gas composition, ash distribution and unbumt carbon in ash were determined for the combustion of the five biomass fuels (Table 3). Key observations from the combustion tests were ... 

Fuel panicle size and excess air also affect the extent of combustion as more unbumt carbon in the bottom and fly (cyclone) ash was derived from combustion of the off-cuts with sawdust (RPO) and E. nitens steam treated (ENT), both of which involved more fine (or fibre) particles and lower excess air. 

Shimoda, M., Sugano, A., Kimura, T., Watanabe, Y., and Ishiyama, K. "Prediction Method of Unbumt Carbon for Coal Fired Utility Boiler Using Image Processing Technique of Combustion Flame." IEEE Transactions on Energy Conversion 5 (1990) 640-45. 

As the sulfur contained in the coal reacts with the limestone to form gypsum, the ash removed tiom the bottom of the reactor apart from the original coal ash contains only CaS04 and small amounts of lime and unbumt carbon. It can be harmlessly disposed of. 

This does not mean, however, that diesel exhaust requires no aftertreatment. A negative feature of diesel motors is that the flame front is cooled before all the fuel is oxidized. This leads to the generation of particulate matter (PM), a mixture of unbumt carbon, organic species, sulfates and oil additives. Small particles of PM (<2.5pm) have been shown to deposit in the lungs and to have significant adverse health consequences. PM reduction is, as a result, by far the most important goal of diesel after-treatment. 

It may be noted that the hot gas filters not only minimized deposition of dust particles in the catalyst beds but also increased the heat capacity of the conversion system. In the case of a long plant stoppage, there could be more heat retention in the plant when blinds are inserted in the gas inlet line of the HGF. The unit would also protect the top layer of the first pass catalyst from any soot/unbumt carbon particles during plant start-up (during commissioning or after an annual shutdown.)... 

The authors also propose a CFB reactor set-up for CLC operation with solid fuels (see Figure 4). A high velocity riser is suggested for the oxidizer, and a down-flow moving bed or bubbling fluidized bed for the reducer in which the solid fuel is fed. A low-velocity bubbling bed or turbulent fluidized bed thus acts as deep reduction reactor and separator for oxygen carriers from fly ash and unbumt carbon. In this... 

An array of many individual burner elements is used in industrial boilers, and various postflame combustion control systems, such as overfire air, staging air, re-buming systems, and selective non-catalytic reduction systems, can be employed in the post-flame zone to enhance the efficiency. Emissions of carbon monoxide, unbumt carbon, nitrous oxides, or sulfur dioxide are monitored to ensure the compliance with... 

After implementing a number of modifications in order to improve the thermal behaviour of the first cyclone, experiments were done with low excess air levels but this resulted in high elutriation rates of unbumt carbon, which coimteracted the beneficial... 

For the evaluation of the importance of carbon content on the adsorption behavioiu, we will separate a sample into several size fractions, in order to preconcentrate the fly coke. It was found, however, that many carbon particles are larger than any other component of the apeldoom fly ash TNO 3. So, the fraction of particles>180 pm mostly contains unbumt carbon particles. Separation and analysis of this fraction, after spiking the fly ash, may answer the question of preferred adsorption of PAH onto carbon. 

The presence of unbumt carbon in fly ashes has many adverse effects on concrete including the appearance of grayish blackness in mortars and concrete, need for higher w/c+f ratio to obtain required consistency, and decreased air entertainment. Thermogravimetric analysis has been developed to estimate hydrated lime, calcium carbonate, and unbumed carbon in fly ashes.The methodology is as follows ... 

Lean-bum engines are more fuel-efficient when there is an excess of oxygen in the combustion gas and emit less carbon dioxide per mile travelled. Lean conditions lead to lower levels of NOx in the exhaust gas, but the introduction of future legislation on the NOx content of the exhaust will require that further reduction will have to be considered. NOx removal in the presence of excess oxygen is more difficult than removal under stoichiometric conditions because normally the NOx is reduced by some of the unbumt carbon monoxide and hydrocarbons in the exhaust. 

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