Air-fuel firing

Now, let us list the major differences of air/fuel and oxy/fuel firing. Air/fuel firing includes nitrogen in the combustion zone. The following relation can be offered to calculate the volume difference in the case of methane combustion for air/fuel and oxy/fuel firing modes ... 

The Tg of a commercial soda-lime-silicate glass which was melted in an older, air-fuel fired tank, which contains about 350 wtppm of water, is typically 5 to 7 K greater than that of the same glass produced by the same manufacturer in an oxygen-fuel tank. Remelting a commercial... 

The convection heat transfer will be lower because lower volume means lower velocity. But convection is a minor fraction of the total heat transfer in furnaces above about 1200 F (650 C). Because about the same amount of chemical energy is released with oxy-fuel firing as with air-fuel firing, the adiabatic flame temperature as well as the triatomic gas radiation intensity from the poc of oxy-fuel firing will be higher. 

Heat/Solvent Recovery. The primary appHcation of heat pipes in the chemical industry is for combustion air preheat on various types of process furnaces which simultaneously increases furnace efficiency and throughput and conserves fuel. Advantages include modular design, isothermal tube temperature eliminating cold corner corrosion, high thermal effectiveness, high reHabiHty and options for removable tubes, alternative materials and arrangements, and replacement or add-on sections for increased performance (see Furnaces, fuel-FIREd). 

The inside of the convection tubes rarely foul, but occasionally the Hquid unsaturates in feedstocks tend to polymerize and stick to the walls and thus reduce the heat transfer. This soft coke is normally removed by mechanical means. In limited cases, the coke can also be burnt off with air and steam. Normally, the outside surface of the convection section fouls due to dust and particles in the flue gas. Periodically (6 to 36 months), the outside surface is cleaned by steam lancing. With Hquid fuel firing, the surface may require more frequent cleaning. 

Supplementary fuel firing in boilers Energy in the form of steam Shredding, air separation, magnetic separation If least capital investment desired, existing boiler required to he capable of modification air-quality regulations possibly prohibiting use... 

FIG. 27-11 Gomtilstion air requirements for various fuels at zero excess air. To convert from kg air/GJ fired to Ih air/lO Btii fired, multiply hy 2.090. 

Langford, B., Palmer, K. N., and Tonkin, P. S. 1961. The Performance of Flame Arrestors Against Flame Propagating m Various Fuel/Air Mixtures. Fire Research Station Note No. 486. Fire Research Station, Borehamwood, Herts., England. 

Liquid Pool Flames. Liquid fuel or flammable spills often lead to fires involving a flame at the surface of the liquid. This type of diffusion flame moves across the surface of the liquid driven by evaporation of the fuel through heat transfer ahead of the flame. If the liquid pool or spill is formed at ambient conditions sufficient to vaporize enough fuel to form a flammable air/fuel mixture, then a flame can propagate through the mixture above the spill as a premixed flame. 

Gas transport properties for the products of combustion of the common fuels, fired at normal excess air at or nearfull boiler load, may be obtained from Tables 23.1-23.4. Non-luminous gas radiation has a small overall effect in the convective section, typically 2-5 per cent of total convection. It may therefore be neglected for a conservative calculation. 

Early SM boilers were manufactured with between two and four corrugated furnace tubes in wet-back and dry-back versions and generally incorporated heat recovery equipment such as economizers and air heaters. Some designs also provided for superheaters and for coal, oil, or gas fuel firing. Many of the best features are incorporated in the SM boilers commonly available today. 

A room has mass flow rates of fuel, air and fire products at an instant of time in the fire, as shown in the sketch. 

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